diff --git a/apps/files_sharing/tests/activity.php b/apps/files_sharing/tests/activity.php
index b3575b0b70..40a1031f77 100644
--- a/apps/files_sharing/tests/activity.php
+++ b/apps/files_sharing/tests/activity.php
@@ -41,11 +41,13 @@ class Activity extends \OCA\Files_Sharing\Tests\TestCase {
 	protected function setUp() {
 		parent::setUp();
 		$this->activity = new \OCA\Files_Sharing\Activity(
-			$this->getMock('\OC\L10N\Factory'),
-			$this->getMockBuilder('\OCP\IURLGenerator')
+			$this->getMockBuilder('OCP\L10N\IFactory')
 				->disableOriginalConstructor()
 				->getMock(),
-			$this->getMockBuilder('\OCP\Activity\IManager')
+			$this->getMockBuilder('OCP\IURLGenerator')
+				->disableOriginalConstructor()
+				->getMock(),
+			$this->getMockBuilder('OCP\Activity\IManager')
 				->disableOriginalConstructor()
 				->getMock()
 		);
diff --git a/core/js/config.php b/core/js/config.php
index 0670df60ab..708da777ee 100644
--- a/core/js/config.php
+++ b/core/js/config.php
@@ -67,7 +67,7 @@ $array = array(
 	"oc_isadmin" => OC_User::isAdminUser(OC_User::getUser()) ? 'true' : 'false',
 	"oc_webroot" => "\"".OC::$WEBROOT."\"",
 	"oc_appswebroots" =>  str_replace('\\/', '/', json_encode($apps_paths)), // Ugly unescape slashes waiting for better solution
-	"datepickerFormatDate" => json_encode($l->getDateFormat()),
+	"datepickerFormatDate" => json_encode($l->l('jsdate', null)),
 	"dayNames" =>  json_encode(
 		array(
 			(string)$l->t('Sunday'),
@@ -133,7 +133,7 @@ $array = array(
 			(string)$l->t('Dec.')
 		)
 	),
-	"firstDay" => json_encode($l->getFirstWeekDay()) ,
+	"firstDay" => json_encode($l->l('firstday', null)) ,
 	"oc_config" => json_encode(
 		array(
 			'session_lifetime'	=> min(\OCP\Config::getSystemValue('session_lifetime', OC::$server->getIniWrapper()->getNumeric('session.gc_maxlifetime')), OC::$server->getIniWrapper()->getNumeric('session.gc_maxlifetime')),
diff --git a/lib/private/l10n/factory.php b/lib/private/l10n/factory.php
index c3c7cc21bb..09496cba41 100644
--- a/lib/private/l10n/factory.php
+++ b/lib/private/l10n/factory.php
@@ -25,16 +25,48 @@
 
 namespace OC\L10N;
 
+use OCP\IConfig;
+use OCP\IRequest;
 use OCP\L10N\IFactory;
 
 /**
  * A factory that generates language instances
  */
 class Factory implements IFactory {
+
+	/** @var string */
+	protected $requestLanguage = '';
+
 	/**
 	 * cached instances
+	 * @var array Structure: Lang => App => \OCP\IL10N
 	 */
-	protected $instances = array();
+	protected $instances = [];
+
+	/**
+	 * @var array Structure: App => string[]
+	 */
+	protected $availableLanguages = [];
+
+	/**
+	 * @var array Structure: string => callable
+	 */
+	protected $pluralFunctions = [];
+
+	/** @var IConfig */
+	protected $config;
+
+	/** @var IRequest */
+	protected $request;
+
+	/**
+	 * @param IConfig $config
+	 * @param IRequest $request
+	 */
+	public function __construct(IConfig $config, IRequest $request) {
+		$this->config = $config;
+		$this->request = $request;
+	}
 
 	/**
 	 * Get a language instance
@@ -44,16 +76,269 @@ class Factory implements IFactory {
 	 * @return \OCP\IL10N
 	 */
 	public function get($app, $lang = null) {
+		$app = \OC_App::cleanAppId($app);
+		if ($lang !== null) {
+			$lang = str_replace(array('\0', '/', '\\', '..'), '', (string) $lang);
+		}
 		$key = $lang;
-		if ($key === null) {
+		if ($key === null || !$this->languageExists($app, $lang)) {
 			$key = 'null';
+			$lang = $this->findLanguage($app);
 		}
 
 		if (!isset($this->instances[$key][$app])) {
-			$this->instances[$key][$app] = new \OC_L10N($app, $lang);
+			$this->instances[$key][$app] = new L10N(
+				$this, $app, $lang,
+				$this->getL10nFilesForApp($app, $lang)
+			);
 		}
 
 		return $this->instances[$key][$app];
 	}
 
+	/**
+	 * Find the best language
+	 *
+	 * @param string|null $app App id or null for core
+	 * @return string language If nothing works it returns 'en'
+	 */
+	public function findLanguage($app = null) {
+		if ($this->requestLanguage !== '' && $this->languageExists($app, $this->requestLanguage)) {
+			return $this->requestLanguage;
+		}
+
+		$userId = \OC_User::getUser(); // FIXME not available in non-static?
+
+		$userLang = $userId !== false ? $this->config->getUserValue($userId, 'core', 'lang') : null;
+		if ($userLang) {
+			$this->requestLanguage = $userLang;
+			if ($this->languageExists($app, $userLang)) {
+				return $userLang;
+			}
+		}
+
+		$defaultLanguage = $this->config->getSystemValue('default_language', false);
+
+		if ($defaultLanguage !== false && $this->languageExists($app, $defaultLanguage)) {
+			return $defaultLanguage;
+		}
+
+		$lang = $this->setLanguageFromRequest($app);
+		if ($userId !== false && $app === null && !$userLang) {
+			$this->config->setUserValue($userId, 'core', 'lang', $lang);
+		}
+
+		return $lang;
+	}
+
+	/**
+	 * Find all available languages for an app
+	 *
+	 * @param string|null $app App id or null for core
+	 * @return array an array of available languages
+	 */
+	public function findAvailableLanguages($app = null) {
+		$key = $app;
+		if ($key === null) {
+			$key = 'null';
+		}
+
+		// also works with null as key
+		if (!empty($this->availableLanguages[$key])) {
+			return $this->availableLanguages[$key];
+		}
+
+		$available = ['en']; //english is always available
+		$dir = $this->findL10nDir($app);
+		if (is_dir($dir)) {
+			$files = scandir($dir);
+			if ($files !== false) {
+				foreach ($files as $file) {
+					if (substr($file, -5) === '.json' && substr($file, 0, 4) !== 'l10n') {
+						$available[] = substr($file, 0, -5);
+					}
+				}
+			}
+		}
+
+		$this->availableLanguages[$key] = $available;
+		return $available;
+	}
+
+	/**
+	 * @param string|null $app App id or null for core
+	 * @param string $lang
+	 * @return bool
+	 */
+	public function languageExists($app, $lang) {
+		if ($lang === 'en') {//english is always available
+			return true;
+		}
+
+		$languages = $this->findAvailableLanguages($app);
+		return array_search($lang, $languages) !== false;
+	}
+
+	/**
+	 * @param string|null $app App id or null for core
+	 * @return string
+	 */
+	public function setLanguageFromRequest($app = null) {
+		$header = $this->request->getHeader('ACCEPT_LANGUAGE');
+		if ($header) {
+			$available = $this->findAvailableLanguages($app);
+
+			// E.g. make sure that 'de' is before 'de_DE'.
+			sort($available);
+
+			$preferences = preg_split('/,\s*/', strtolower($header));
+			foreach ($preferences as $preference) {
+				list($preferred_language) = explode(';', $preference);
+				$preferred_language = str_replace('-', '_', $preferred_language);
+
+				foreach ($available as $available_language) {
+					if ($preferred_language === strtolower($available_language)) {
+						if ($app === null && !$this->requestLanguage) {
+							$this->requestLanguage = $available_language;
+						}
+						return $available_language;
+					}
+				}
+
+				// Fallback from de_De to de
+				foreach ($available as $available_language) {
+					if (substr($preferred_language, 0, 2) === $available_language) {
+						if ($app === null && !$this->requestLanguage) {
+							$this->requestLanguage = $available_language;
+						}
+						return $available_language;
+					}
+				}
+			}
+		}
+
+		if (!$this->requestLanguage) {
+			$this->requestLanguage = 'en';
+		}
+		return 'en'; // Last try: English
+	}
+
+	/**
+	 * Get a list of language files that should be loaded
+	 *
+	 * @param string $app
+	 * @param string $lang
+	 * @return string[]
+	 */
+	// FIXME This method is only public, until OC_L10N does not need it anymore,
+	// FIXME This is also the reason, why it is not in the public interface
+	public function getL10nFilesForApp($app, $lang) {
+		$languageFiles = [];
+
+		$i18nDir = $this->findL10nDir($app);
+		$transFile = strip_tags($i18nDir) . strip_tags($lang) . '.json';
+
+		if ((\OC_Helper::isSubDirectory($transFile, \OC::$SERVERROOT . '/core/l10n/')
+				|| \OC_Helper::isSubDirectory($transFile, \OC::$SERVERROOT . '/lib/l10n/')
+				|| \OC_Helper::isSubDirectory($transFile, \OC::$SERVERROOT . '/settings/l10n/')
+				|| \OC_Helper::isSubDirectory($transFile, \OC_App::getAppPath($app) . '/l10n/')
+			)
+			&& file_exists($transFile)) {
+			// load the translations file
+			$languageFiles[] = $transFile;
+
+			// merge with translations from theme
+			$theme = $this->config->getSystemValue('theme');
+			if (!empty($theme)) {
+				$transFile = \OC::$SERVERROOT . '/themes/' . $theme . substr($transFile, strlen(\OC::$SERVERROOT));
+				if (file_exists($transFile)) {
+					$languageFiles[] = $transFile;
+				}
+			}
+		}
+
+		return $languageFiles;
+	}
+
+	/**
+	 * find the l10n directory
+	 *
+	 * @param string $app App id or empty string for core
+	 * @return string directory
+	 */
+	protected function findL10nDir($app = null) {
+		if (in_array($app, ['core', 'lib', 'settings'])) {
+			if (file_exists(\OC::$SERVERROOT . '/' . $app . '/l10n/')) {
+				return \OC::$SERVERROOT . '/' . $app . '/l10n/';
+			}
+		} else if ($app && \OC_App::getAppPath($app) !== false) {
+			// Check if the app is in the app folder
+			return \OC_App::getAppPath($app) . '/l10n/';
+		}
+		return \OC::$SERVERROOT . '/core/l10n/';
+	}
+
+
+	/**
+	 * Creates a function from the plural string
+	 *
+	 * Parts of the code is copied from Habari:
+	 * https://github.com/habari/system/blob/master/classes/locale.php
+	 * @param string $string
+	 * @return string
+	 */
+	public function createPluralFunction($string) {
+		if (isset($this->pluralFunctions[$string])) {
+			return $this->pluralFunctions[$string];
+		}
+
+		if (preg_match( '/^\s*nplurals\s*=\s*(\d+)\s*;\s*plural=(.*)$/u', $string, $matches)) {
+			// sanitize
+			$nplurals = preg_replace( '/[^0-9]/', '', $matches[1] );
+			$plural = preg_replace( '#[^n0-9:\(\)\?\|\&=!<>+*/\%-]#', '', $matches[2] );
+
+			$body = str_replace(
+				array( 'plural', 'n', '$n$plurals', ),
+				array( '$plural', '$n', '$nplurals', ),
+				'nplurals='. $nplurals . '; plural=' . $plural
+			);
+
+			// add parents
+			// important since PHP's ternary evaluates from left to right
+			$body .= ';';
+			$res = '';
+			$p = 0;
+			for($i = 0; $i < strlen($body); $i++) {
+				$ch = $body[$i];
+				switch ( $ch ) {
+					case '?':
+						$res .= ' ? (';
+						$p++;
+						break;
+					case ':':
+						$res .= ') : (';
+						break;
+					case ';':
+						$res .= str_repeat( ')', $p ) . ';';
+						$p = 0;
+						break;
+					default:
+						$res .= $ch;
+				}
+			}
+
+			$body = $res . 'return ($plural>=$nplurals?$nplurals-1:$plural);';
+			$function = create_function('$n', $body);
+			$this->pluralFunctions[$string] = $function;
+			return $function;
+		} else {
+			// default: one plural form for all cases but n==1 (english)
+			$function = create_function(
+				'$n',
+				'$nplurals=2;$plural=($n==1?0:1);return ($plural>=$nplurals?$nplurals-1:$plural);'
+			);
+			$this->pluralFunctions[$string] = $function;
+			return $function;
+		}
+	}
 }
diff --git a/lib/private/l10n/l10n.php b/lib/private/l10n/l10n.php
new file mode 100644
index 0000000000..3e999e8c67
--- /dev/null
+++ b/lib/private/l10n/l10n.php
@@ -0,0 +1,216 @@
+<?php
+/**
+ * @author Joas Schilling <nickvergessen@owncloud.com>
+ *
+ * @copyright Copyright (c) 2016, ownCloud, Inc.
+ * @license AGPL-3.0
+ *
+ * This code is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License, version 3,
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License, version 3,
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ *
+ */
+
+namespace OC\L10N;
+
+use OCP\IL10N;
+use OCP\L10N\IFactory;
+use Punic\Calendar;
+
+class L10N implements IL10N {
+
+	/** @var IFactory */
+	protected $factory;
+
+	/** @var string App of this object */
+	protected $app;
+
+	/** @var string Language of this object */
+	protected $lang;
+
+	/** @var string Plural forms (string) */
+	private $pluralFormString = 'nplurals=2; plural=(n != 1);';
+
+	/** @var string Plural forms (function) */
+	private $pluralFormFunction = null;
+
+	/** @var string[] */
+	private $translations = [];
+
+	/**
+	 * @param IFactory $factory
+	 * @param string $app
+	 * @param string $lang
+	 * @param array $files
+	 */
+	public function __construct(IFactory $factory, $app, $lang, array $files) {
+		$this->factory = $factory;
+		$this->app = $app;
+		$this->lang = $lang;
+
+		$this->translations = [];
+		foreach ($files as $languageFile) {
+			$this->load($languageFile);
+		}
+	}
+
+	/**
+	 * The code (en, de, ...) of the language that is used for this instance
+	 *
+	 * @return string language
+	 */
+	public function getLanguageCode() {
+		return $this->lang;
+	}
+
+	/**
+	 * Translating
+	 * @param string $text The text we need a translation for
+	 * @param array $parameters default:array() Parameters for sprintf
+	 * @return string Translation or the same text
+	 *
+	 * Returns the translation. If no translation is found, $text will be
+	 * returned.
+	 */
+	public function t($text, $parameters = array()) {
+		return (string) new \OC_L10N_String($this, $text, $parameters);
+	}
+
+	/**
+	 * Translating
+	 * @param string $text_singular the string to translate for exactly one object
+	 * @param string $text_plural the string to translate for n objects
+	 * @param integer $count Number of objects
+	 * @param array $parameters default:array() Parameters for sprintf
+	 * @return string Translation or the same text
+	 *
+	 * Returns the translation. If no translation is found, $text will be
+	 * returned. %n will be replaced with the number of objects.
+	 *
+	 * The correct plural is determined by the plural_forms-function
+	 * provided by the po file.
+	 *
+	 */
+	public function n($text_singular, $text_plural, $count, $parameters = array()) {
+		$identifier = "_${text_singular}_::_${text_plural}_";
+		if (isset($this->translations[$identifier])) {
+			return (string) new \OC_L10N_String($this, $identifier, $parameters, $count);
+		} else {
+			if ($count === 1) {
+				return (string) new \OC_L10N_String($this, $text_singular, $parameters, $count);
+			} else {
+				return (string) new \OC_L10N_String($this, $text_plural, $parameters, $count);
+			}
+		}
+	}
+
+	/**
+	 * Localization
+	 * @param string $type Type of localization
+	 * @param \DateTime|int|string $data parameters for this localization
+	 * @param array $options
+	 * @return string|int|false
+	 *
+	 * Returns the localized data.
+	 *
+	 * Implemented types:
+	 *  - date
+	 *    - Creates a date
+	 *    - params: timestamp (int/string)
+	 *  - datetime
+	 *    - Creates date and time
+	 *    - params: timestamp (int/string)
+	 *  - time
+	 *    - Creates a time
+	 *    - params: timestamp (int/string)
+	 *  - firstday: Returns the first day of the week (0 sunday - 6 saturday)
+	 *  - jsdate: Returns the short JS date format
+	 */
+	public function l($type, $data = null, $options = array()) {
+		// Use the language of the instance
+		$locale = $this->getLanguageCode();
+		if ($locale === 'sr@latin') {
+			$locale = 'sr_latn';
+		}
+
+		if ($type === 'firstday') {
+			return (int) Calendar::getFirstWeekday($locale);
+		}
+		if ($type === 'jsdate') {
+			return (string) Calendar::getDateFormat('short', $locale);
+		}
+
+		$value = new \DateTime();
+		if ($data instanceof \DateTime) {
+			$value = $data;
+		} else if (is_string($data) && !is_numeric($data)) {
+			$data = strtotime($data);
+			$value->setTimestamp($data);
+		} else if ($data !== null) {
+			$value->setTimestamp($data);
+		}
+
+		$options = array_merge(array('width' => 'long'), $options);
+		$width = $options['width'];
+		switch ($type) {
+			case 'date':
+				return (string) Calendar::formatDate($value, $width, $locale);
+			case 'datetime':
+				return (string) Calendar::formatDatetime($value, $width, $locale);
+			case 'time':
+				return (string) Calendar::formatTime($value, $width, $locale);
+			default:
+				return false;
+		}
+	}
+
+	/**
+	 * Returns an associative array with all translations
+	 *
+	 * Called by \OC_L10N_String
+	 * @return array
+	 */
+	public function getTranslations() {
+		return $this->translations;
+	}
+
+	/**
+	 * Returnsed function accepts the argument $n
+	 *
+	 * Called by \OC_L10N_String
+	 * @return string the plural form function
+	 */
+	public function getPluralFormFunction() {
+		if (is_null($this->pluralFormFunction)) {
+			$this->pluralFormFunction = $this->factory->createPluralFunction($this->pluralFormString);
+		}
+		return $this->pluralFormFunction;
+	}
+
+	/**
+	 * @param $translationFile
+	 * @return bool
+	 */
+	protected function load($translationFile) {
+		$json = json_decode(file_get_contents($translationFile), true);
+		if (!is_array($json)) {
+			$jsonError = json_last_error();
+			\OC::$server->getLogger()->warning("Failed to load $translationFile - json error code: $jsonError", ['app' => 'l10n']);
+			return false;
+		}
+
+		if (!empty($json['pluralForm'])) {
+			$this->pluralFormString = $json['pluralForm'];
+		}
+		$this->translations = array_merge($this->translations, $json['translations']);
+		return true;
+	}
+}
diff --git a/lib/private/l10n/string.php b/lib/private/l10n/string.php
index 84d1603871..9c93b8c5a6 100644
--- a/lib/private/l10n/string.php
+++ b/lib/private/l10n/string.php
@@ -26,28 +26,23 @@
  */
 
 class OC_L10N_String implements JsonSerializable {
-	/**
-	 * @var OC_L10N
-	 */
+	/** @var \OC_L10N|\OC\L10N\L10N */
 	protected $l10n;
 
-	/**
-	 * @var string
-	 */
+	/** @var string */
 	protected $text;
 
-	/**
-	 * @var array
-	 */
+	/** @var array */
 	protected $parameters;
 
-	/**
-	 * @var integer
-	 */
+	/** @var integer */
 	protected $count;
 
 	/**
-	 * @param OC_L10N $l10n
+	 * @param \OC_L10N|\OC\L10N\L10N $l10n
+	 * @param string|string[] $text
+	 * @param array $parameters
+	 * @param int $count
 	 */
 	public function __construct($l10n, $text, $parameters, $count = 1) {
 		$this->l10n = $l10n;
@@ -80,5 +75,4 @@ class OC_L10N_String implements JsonSerializable {
 	public function jsonSerialize() {
 		return $this->__toString();
 	}
-
 }
diff --git a/lib/private/l10n.php b/lib/private/legacy/l10n.php
similarity index 53%
rename from lib/private/l10n.php
rename to lib/private/legacy/l10n.php
index b53fadc2bd..5d5d89100a 100644
--- a/lib/private/l10n.php
+++ b/lib/private/legacy/l10n.php
@@ -37,6 +37,7 @@
 
 /**
  * This class is for i18n and l10n
+ * @deprecated 9.0.0 Use \OC::$server->getL10NFactory()->get() instead
  */
 class OC_L10N implements \OCP\IL10N {
 	/**
@@ -82,56 +83,29 @@ class OC_L10N implements \OCP\IL10N {
 	 *
 	 * If language is not set, the constructor tries to find the right
 	 * language.
+	 * @deprecated 9.0.0 Use \OC::$server->getL10NFactory()->get() instead
 	 */
 	public function __construct($app, $lang = null) {
+		$app = \OC_App::cleanAppId($app);
 		$this->app = $app;
+
+		if ($lang !== null) {
+			$lang = str_replace(array('\0', '/', '\\', '..'), '', $lang);
+		}
+
+		// Find the right language
+		if ($app !== 'test' && !\OC::$server->getL10NFactory()->languageExists($app, $lang)) {
+			$lang = \OC::$server->getL10NFactory()->findLanguage($app);
+		}
+
 		$this->lang = $lang;
 	}
 
-	/**
-	 * @return string
-	 */
-	public static function setLanguageFromRequest() {
-		if (isset($_SERVER['HTTP_ACCEPT_LANGUAGE'])) {
-			$available = self::findAvailableLanguages();
-
-			// E.g. make sure that 'de' is before 'de_DE'.
-			sort($available);
-
-			$preferences = preg_split('/,\s*/', strtolower($_SERVER['HTTP_ACCEPT_LANGUAGE']));
-			foreach ($preferences as $preference) {
-				list($preferred_language) = explode(';', $preference);
-				$preferred_language = str_replace('-', '_', $preferred_language);
-				foreach ($available as $available_language) {
-					if ($preferred_language === strtolower($available_language)) {
-						if (!self::$language) {
-							self::$language = $available_language;
-						}
-						return $available_language;
-					}
-				}
-				foreach ($available as $available_language) {
-					if (substr($preferred_language, 0, 2) === $available_language) {
-						if (!self::$language) {
-							self::$language = $available_language;
-						}
-						return $available_language;
-					}
-				}
-			}
-		}
-
-		self::$language = 'en';
-		// Last try: English
-		return 'en';
-	}
-
 	/**
 	 * @param $transFile
-	 * @param bool $mergeTranslations
 	 * @return bool
 	 */
-	public function load($transFile, $mergeTranslations = false) {
+	public function load($transFile) {
 		$this->app = true;
 
 		$json = json_decode(file_get_contents($transFile), true);
@@ -144,11 +118,7 @@ class OC_L10N implements \OCP\IL10N {
 		$this->pluralFormString = $json['pluralForm'];
 		$translations = $json['translations'];
 
-		if ($mergeTranslations) {
-			$this->translations = array_merge($this->translations, $translations);
-		} else {
-			$this->translations = $translations;
-		}
+		$this->translations = array_merge($this->translations, $translations);
 
 		return true;
 	}
@@ -157,101 +127,17 @@ class OC_L10N implements \OCP\IL10N {
 		if ($this->app === true) {
 			return;
 		}
-		$app = OC_App::cleanAppId($this->app);
-		$lang = str_replace(array('\0', '/', '\\', '..'), '', $this->lang);
+		$app = $this->app;
+		$lang = $this->lang;
 		$this->app = true;
-		// Find the right language
-		if(is_null($lang) || $lang == '') {
-			$lang = self::findLanguage($app);
-		}
 
-		// Use cache if possible
-		if(array_key_exists($app.'::'.$lang, self::$cache)) {
-			$this->translations = self::$cache[$app.'::'.$lang]['t'];
-		} else{
-			$i18nDir = self::findI18nDir($app);
-			$transFile = strip_tags($i18nDir).strip_tags($lang).'.json';
-			// Texts are in $i18ndir
-			// (Just no need to define date/time format etc. twice)
-			if((OC_Helper::isSubDirectory($transFile, OC::$SERVERROOT.'/core/l10n/')
-				|| OC_Helper::isSubDirectory($transFile, OC::$SERVERROOT.'/lib/l10n/')
-				|| OC_Helper::isSubDirectory($transFile, OC::$SERVERROOT.'/settings')
-				|| OC_Helper::isSubDirectory($transFile, OC_App::getAppPath($app).'/l10n/')
-				)
-				&& file_exists($transFile)) {
-				// load the translations file
-				if($this->load($transFile)) {
-					//merge with translations from theme
-					$theme = \OC::$server->getConfig()->getSystemValue('theme');
-					if (!empty($theme)) {
-						$transFile = OC::$SERVERROOT.'/themes/'.$theme.substr($transFile, strlen(OC::$SERVERROOT));
-						if (file_exists($transFile)) {
-							$this->load($transFile, true);
-						}
-					}
-				}
-			}
+		/** @var \OC\L10N\Factory $factory */
+		$factory = \OC::$server->getL10NFactory();
+		$languageFiles = $factory->getL10nFilesForApp($app, $lang);
 
-			self::$cache[$app.'::'.$lang]['t'] = $this->translations;
-		}
-	}
-
-	/**
-	 * Creates a function that The constructor
-	 *
-	 * If language is not set, the constructor tries to find the right
-	 * language.
-	 *
-	 * Parts of the code is copied from Habari:
-	 * https://github.com/habari/system/blob/master/classes/locale.php
-	 * @param string $string
-	 * @return string
-	 */
-	protected function createPluralFormFunction($string){
-		if(preg_match( '/^\s*nplurals\s*=\s*(\d+)\s*;\s*plural=(.*)$/u', $string, $matches)) {
-			// sanitize
-			$nplurals = preg_replace( '/[^0-9]/', '', $matches[1] );
-			$plural = preg_replace( '#[^n0-9:\(\)\?\|\&=!<>+*/\%-]#', '', $matches[2] );
-
-			$body = str_replace(
-				array( 'plural', 'n', '$n$plurals', ),
-				array( '$plural', '$n', '$nplurals', ),
-				'nplurals='. $nplurals . '; plural=' . $plural
-			);
-
-			// add parents
-			// important since PHP's ternary evaluates from left to right
-			$body .= ';';
-			$res = '';
-			$p = 0;
-			for($i = 0; $i < strlen($body); $i++) {
-				$ch = $body[$i];
-				switch ( $ch ) {
-				case '?':
-					$res .= ' ? (';
-					$p++;
-					break;
-				case ':':
-					$res .= ') : (';
-					break;
-				case ';':
-					$res .= str_repeat( ')', $p ) . ';';
-					$p = 0;
-					break;
-				default:
-					$res .= $ch;
-				}
-			}
-
-			$body = $res . 'return ($plural>=$nplurals?$nplurals-1:$plural);';
-			return create_function('$n', $body);
-		}
-		else {
-			// default: one plural form for all cases but n==1 (english)
-			return create_function(
-				'$n',
-				'$nplurals=2;$plural=($n==1?0:1);return ($plural>=$nplurals?$nplurals-1:$plural);'
-			);
+		$this->translations = [];
+		foreach ($languageFiles as $languageFile) {
+			$this->load($languageFile);
 		}
 	}
 
@@ -316,8 +202,8 @@ class OC_L10N implements \OCP\IL10N {
 	 */
 	public function getPluralFormFunction() {
 		$this->init();
-		if(is_null($this->pluralFormFunction)) {
-			$this->pluralFormFunction = $this->createPluralFormFunction($this->pluralFormString);
+		if (is_null($this->pluralFormFunction)) {
+			$this->pluralFormFunction = \OC::$server->getL10NFactory()->createPluralFunction($this->pluralFormString);
 		}
 		return $this->pluralFormFunction;
 	}
@@ -341,6 +227,8 @@ class OC_L10N implements \OCP\IL10N {
 	 *  - time
 	 *    - Creates a time
 	 *    - params: timestamp (int/string)
+	 *  - firstday: Returns the first day of the week (0 sunday - 6 saturday)
+	 *  - jsdate: Returns the short JS date format
 	 */
 	public function l($type, $data, $options = array()) {
 		if ($type === 'firstday') {
@@ -361,12 +249,8 @@ class OC_L10N implements \OCP\IL10N {
 			$value->setTimestamp($data);
 		}
 
-		// Use the language of the instance, before falling back to the current user's language
-		$locale = $this->lang;
-		if ($locale === null) {
-			$locale = self::findLanguage();
-		}
-		$locale = $this->transformToCLDRLocale($locale);
+		// Use the language of the instance
+		$locale = $this->transformToCLDRLocale($this->getLanguageCode());
 
 		$options = array_merge(array('width' => 'long'), $options);
 		$width = $options['width'];
@@ -388,7 +272,38 @@ class OC_L10N implements \OCP\IL10N {
 	 * @return string language
 	 */
 	public function getLanguageCode() {
-		return $this->lang ? $this->lang : self::findLanguage();
+		return $this->lang;
+	}
+
+	/**
+	 * @return string
+	 * @throws \Punic\Exception\ValueNotInList
+	 * @deprecated 9.0.0 Use $this->l('jsdate', null) instead
+	 */
+	public function getDateFormat() {
+		$locale = $this->transformToCLDRLocale($this->getLanguageCode());
+		return Punic\Calendar::getDateFormat('short', $locale);
+	}
+
+	/**
+	 * @return int
+	 * @deprecated 9.0.0 Use $this->l('firstday', null) instead
+	 */
+	public function getFirstWeekDay() {
+		$locale = $this->transformToCLDRLocale($this->getLanguageCode());
+		return Punic\Calendar::getFirstWeekday($locale);
+	}
+
+	/**
+	 * @param string $locale
+	 * @return string
+	 */
+	private function transformToCLDRLocale($locale) {
+		if ($locale === 'sr@latin') {
+			return 'sr_latn';
+		}
+
+		return $locale;
 	}
 
 	/**
@@ -397,123 +312,37 @@ class OC_L10N implements \OCP\IL10N {
 	 * @return string language
 	 *
 	 * If nothing works it returns 'en'
+	 * @deprecated 9.0.0 Use \OC::$server->getL10NFactory()->findLanguage() instead
 	 */
 	public static function findLanguage($app = null) {
-		if (self::$language != '' && self::languageExists($app, self::$language)) {
-			return self::$language;
-		}
-
-		$config = \OC::$server->getConfig();
-		$userId = \OC_User::getUser();
-
-		if($userId && $config->getUserValue($userId, 'core', 'lang')) {
-			$lang = $config->getUserValue($userId, 'core', 'lang');
-			self::$language = $lang;
-			if(self::languageExists($app, $lang)) {
-				return $lang;
-			}
-		}
-
-		$default_language = $config->getSystemValue('default_language', false);
-
-		if($default_language !== false) {
-			return $default_language;
-		}
-
-		$lang = self::setLanguageFromRequest();
-		if($userId && !$config->getUserValue($userId, 'core', 'lang')) {
-			$config->setUserValue($userId, 'core', 'lang', $lang);
-		}
-
-		return $lang;
+		return \OC::$server->getL10NFactory()->findLanguage($app);
 	}
 
 	/**
-	 * find the l10n directory
-	 * @param string $app App that needs to be translated
-	 * @return string directory
+	 * @return string
+	 * @deprecated 9.0.0 Use \OC::$server->getL10NFactory()->setLanguageFromRequest() instead
 	 */
-	protected static function findI18nDir($app) {
-		// find the i18n dir
-		$i18nDir = OC::$SERVERROOT.'/core/l10n/';
-		if($app != '') {
-			// Check if the app is in the app folder
-			if(file_exists(OC_App::getAppPath($app).'/l10n/')) {
-				$i18nDir = OC_App::getAppPath($app).'/l10n/';
-			}
-			else{
-				$i18nDir = OC::$SERVERROOT.'/'.$app.'/l10n/';
-			}
-		}
-		return $i18nDir;
+	public static function setLanguageFromRequest() {
+		return \OC::$server->getL10NFactory()->setLanguageFromRequest();
 	}
 
 	/**
 	 * find all available languages for an app
 	 * @param string $app App that needs to be translated
 	 * @return array an array of available languages
+	 * @deprecated 9.0.0 Use \OC::$server->getL10NFactory()->findAvailableLanguages() instead
 	 */
 	public static function findAvailableLanguages($app=null) {
-		// also works with null as key
-		if(isset(self::$availableLanguages[$app]) && !empty(self::$availableLanguages[$app])) {
-			return self::$availableLanguages[$app];
-		}
-		$available=array('en');//english is always available
-		$dir = self::findI18nDir($app);
-		if(is_dir($dir)) {
-			$files=scandir($dir);
-			foreach($files as $file) {
-				if(substr($file, -5, 5) === '.json' && substr($file, 0, 4) !== 'l10n') {
-					$i = substr($file, 0, -5);
-					$available[] = $i;
-				}
-			}
-		}
-
-		self::$availableLanguages[$app] = $available;
-		return $available;
+		return \OC::$server->getL10NFactory()->findAvailableLanguages($app);
 	}
 
 	/**
 	 * @param string $app
 	 * @param string $lang
 	 * @return bool
+	 * @deprecated 9.0.0 Use \OC::$server->getL10NFactory()->languageExists() instead
 	 */
 	public static function languageExists($app, $lang) {
-		if ($lang === 'en') {//english is always available
-			return true;
-		}
-		$dir = self::findI18nDir($app);
-		if(is_dir($dir)) {
-			return file_exists($dir.'/'.$lang.'.json');
-		}
-		return false;
-	}
-
-	/**
-	 * @return string
-	 * @throws \Punic\Exception\ValueNotInList
-	 */
-	public function getDateFormat() {
-		$locale = $this->getLanguageCode();
-		$locale = $this->transformToCLDRLocale($locale);
-		return Punic\Calendar::getDateFormat('short', $locale);
-	}
-
-	/**
-	 * @return int
-	 */
-	public function getFirstWeekDay() {
-		$locale = $this->getLanguageCode();
-		$locale = $this->transformToCLDRLocale($locale);
-		return Punic\Calendar::getFirstWeekday($locale);
-	}
-
-	private function transformToCLDRLocale($locale) {
-		if ($locale === 'sr@latin') {
-			return 'sr_latn';
-		}
-
-		return $locale;
+		return \OC::$server->getL10NFactory()->languageExists($app, $lang);
 	}
 }
diff --git a/lib/private/server.php b/lib/private/server.php
index b8f4bdb53f..81929d0c7b 100644
--- a/lib/private/server.php
+++ b/lib/private/server.php
@@ -262,8 +262,11 @@ class Server extends ServerContainer implements IServerContainer {
 		$this->registerService('AppConfig', function (Server $c) {
 			return new \OC\AppConfig($c->getDatabaseConnection());
 		});
-		$this->registerService('L10NFactory', function ($c) {
-			return new \OC\L10N\Factory();
+		$this->registerService('L10NFactory', function (Server $c) {
+			return new \OC\L10N\Factory(
+				$c->getConfig(),
+				$c->getRequest()
+			);
 		});
 		$this->registerService('URLGenerator', function (Server $c) {
 			$config = $c->getConfig();
diff --git a/lib/public/l10n/ifactory.php b/lib/public/l10n/ifactory.php
index fa3f84fa2f..264c971963 100644
--- a/lib/public/l10n/ifactory.php
+++ b/lib/public/l10n/ifactory.php
@@ -33,4 +33,47 @@ interface IFactory {
 	 * @since 8.2.0
 	 */
 	public function get($app, $lang = null);
+
+	/**
+	 * Find the best language
+	 *
+	 * @param string|null $app App id or null for core
+	 * @return string language If nothing works it returns 'en'
+	 * @since 9.0.0
+	 */
+	public function findLanguage($app = null);
+
+	/**
+	 * Find all available languages for an app
+	 *
+	 * @param string|null $app App id or null for core
+	 * @return string[] an array of available languages
+	 * @since 9.0.0
+	 */
+	public function findAvailableLanguages($app = null);
+
+	/**
+	 * @param string|null $app App id or null for core
+	 * @param string $lang
+	 * @return bool
+	 * @since 9.0.0
+	 */
+	public function languageExists($app, $lang);
+
+	/**
+	 * @param string|null $app App id or null for core
+	 * @return string
+	 * @since 9.0.0
+	 */
+	public function setLanguageFromRequest($app = null);
+
+
+	/**
+	 * Creates a function from the plural string
+	 *
+	 * @param string $string
+	 * @return string Unique function name
+	 * @since 9.0.0
+	 */
+	public function createPluralFunction($string);
 }
diff --git a/ocs/v1.php b/ocs/v1.php
index 4371b0b604..39a8f4e468 100644
--- a/ocs/v1.php
+++ b/ocs/v1.php
@@ -46,7 +46,7 @@ try {
 	OC_App::loadApps();
 
 	// force language as given in the http request
-	\OC_L10N::setLanguageFromRequest();
+	\OC::$server->getL10NFactory()->setLanguageFromRequest();
 
 	OC::$server->getRouter()->match('/ocs'.\OC::$server->getRequest()->getRawPathInfo());
 } catch (ResourceNotFoundException $e) {
diff --git a/remote.php b/remote.php
index a145fc4bd8..26203e2df8 100644
--- a/remote.php
+++ b/remote.php
@@ -109,7 +109,7 @@ try {
 	}
 
 	// force language as given in the http request
-	\OC_L10N::setLanguageFromRequest();
+	\OC::$server->getL10NFactory()->setLanguageFromRequest();
 
 	$file=ltrim($file, '/');
 
diff --git a/settings/ajax/setlanguage.php b/settings/ajax/setlanguage.php
index 760d2ca5d7..537a5afe95 100644
--- a/settings/ajax/setlanguage.php
+++ b/settings/ajax/setlanguage.php
@@ -31,7 +31,7 @@ OCP\JSON::callCheck();
 
 // Get data
 if( isset( $_POST['lang'] ) ) {
-	$languageCodes=OC_L10N::findAvailableLanguages();
+	$languageCodes = \OC::$server->getL10NFactory()->findAvailableLanguages();
 	$lang = (string)$_POST['lang'];
 	if(array_search($lang, $languageCodes) or $lang === 'en') {
 		\OC::$server->getConfig()->setUserValue( OC_User::getUser(), 'core', 'lang', $lang );
diff --git a/settings/personal.php b/settings/personal.php
index 11b4f762a3..261a459a92 100644
--- a/settings/personal.php
+++ b/settings/personal.php
@@ -63,7 +63,7 @@ $user = OC::$server->getUserManager()->get(OC_User::getUser());
 $email = $user->getEMailAddress();
 
 $userLang=$config->getUserValue( OC_User::getUser(), 'core', 'lang', OC_L10N::findLanguage() );
-$languageCodes=OC_L10N::findAvailableLanguages();
+$languageCodes = \OC::$server->getL10NFactory()->findAvailableLanguages();
 
 // array of common languages
 $commonLangCodes = array(
diff --git a/tests/lib/l10n/factorytest.php b/tests/lib/l10n/factorytest.php
new file mode 100644
index 0000000000..f632e48e2d
--- /dev/null
+++ b/tests/lib/l10n/factorytest.php
@@ -0,0 +1,310 @@
+<?php
+/**
+ * Copyright (c) 2016 Joas Schilling <nickvergessen@owncloud.com>
+ * This file is licensed under the Affero General Public License version 3 or
+ * later.
+ * See the COPYING-README file.
+ */
+
+namespace Test\L10N;
+
+
+use OC\L10N\Factory;
+use Test\TestCase;
+
+/**
+ * Class FactoryTest
+ *
+ * @package Test\L10N
+ * @group DB
+ */
+class FactoryTest extends TestCase {
+
+	/** @var \OCP\IConfig|\PHPUnit_Framework_MockObject_MockObject */
+	protected $config;
+
+	/** @var \OCP\IRequest|\PHPUnit_Framework_MockObject_MockObject */
+	protected $request;
+
+	public function setUp() {
+		parent::setUp();
+
+		/** @var \OCP\IConfig $request */
+		$this->config = $this->getMockBuilder('OCP\IConfig')
+			->disableOriginalConstructor()
+			->getMock();
+
+		/** @var \OCP\IRequest $request */
+		$this->request = $this->getMockBuilder('OCP\IRequest')
+			->disableOriginalConstructor()
+			->getMock();
+	}
+
+	/**
+	 * @param array $methods
+	 * @return Factory|\PHPUnit_Framework_MockObject_MockObject
+	 */
+	protected function getFactory(array $methods = []) {
+		if (!empty($methods)) {
+			return $this->getMockBuilder('OC\L10N\Factory')
+				->setConstructorArgs([
+					$this->config,
+					$this->request,
+				])
+				->setMethods($methods)
+				->getMock();
+		} else {
+			return new Factory($this->config, $this->request);
+		}
+	}
+
+	public function dataFindLanguage() {
+		return [
+			[null, false, 1, 'de', true, null, null, null, null, null, 'de'],
+			[null, 'test', 2, 'de', false, 'ru', true, null, null, null, 'ru'],
+			[null, 'test', 1, '', null, 'ru', true, null, null, null, 'ru'],
+			[null, 'test', 3, 'de', false, 'ru', false, 'cz', true, null, 'cz'],
+			[null, 'test', 2, '', null, 'ru', false, 'cz', true, null, 'cz'],
+			[null, 'test', 1, '', null, '', null, 'cz', true, null, 'cz'],
+			[null, 'test', 3, 'de', false, 'ru', false, 'cz', false, 'ar', 'ar'],
+			[null, 'test', 2, '', null, 'ru', false, 'cz', false, 'ar', 'ar'],
+			[null, 'test', 1, '', null, '', null, 'cz', false, 'ar', 'ar'],
+			[null, 'test', 0, '', null, '', null, false, null, 'ar', 'ar'],
+		];
+	}
+
+	/**
+	 * @dataProvider dataFindLanguage
+	 *
+	 * @param string|null $app
+	 * @param string|null $user
+	 * @param int $existsCalls
+	 * @param string $storedRequestLang
+	 * @param bool $srlExists
+	 * @param string|null $userLang
+	 * @param bool $ulExists
+	 * @param string|false $defaultLang
+	 * @param bool $dlExists
+	 * @param string|null $requestLang
+	 * @param string $expected
+	 */
+	public function testFindLanguage($app, $user, $existsCalls, $storedRequestLang, $srlExists, $userLang, $ulExists, $defaultLang, $dlExists, $requestLang, $expected) {
+		$factory = $this->getFactory([
+			'languageExists',
+			'setLanguageFromRequest',
+		]);
+
+		$session = $this->getMockBuilder('OCP\ISession')
+			->disableOriginalConstructor()
+			->getMock();
+		$session->expects($this->any())
+			->method('get')
+			->with('user_id')
+			->willReturn($user);
+		$userSession = $this->getMockBuilder('OC\User\Session')
+			->disableOriginalConstructor()
+			->getMock();
+		$userSession->expects($this->any())
+			->method('getSession')
+			->willReturn($session);
+
+		$this->invokePrivate($factory, 'requestLanguage', [$storedRequestLang]);
+
+		$factory->expects($this->exactly($existsCalls))
+			->method('languageExists')
+			->willReturnMap([
+				[$app, $storedRequestLang, $srlExists],
+				[$app, $userLang, $ulExists],
+				[$app, $defaultLang, $dlExists],
+			]);
+
+		$factory->expects($requestLang !== null ? $this->once() : $this->never())
+			->method('setLanguageFromRequest')
+			->willReturn($requestLang);
+
+		$this->config->expects($userLang !== null ? $this->any() : $this->never())
+			->method('getUserValue')
+			->with($this->anything(), 'core', 'lang')
+			->willReturn($userLang);
+
+		$this->config->expects($defaultLang !== null ? $this->once() : $this->never())
+			->method('getSystemValue')
+			->with('default_language', false)
+			->willReturn($defaultLang);
+
+		$this->overwriteService('UserSession', $userSession);
+		$this->assertSame($expected, $factory->findLanguage($app));
+		$this->restoreService('UserSession');
+	}
+
+	public function dataFindAvailableLanguages() {
+		return [
+			[null],
+			['files'],
+		];
+	}
+
+	/**
+	 * @dataProvider dataFindAvailableLanguages
+	 *
+	 * @param string|null $app
+	 */
+	public function testFindAvailableLanguages($app) {
+		$factory = $this->getFactory(['findL10nDir']);
+		$factory->expects($this->once())
+			->method('findL10nDir')
+			->with($app)
+			->willReturn(\OC::$SERVERROOT . '/tests/data/l10n/');
+
+		$this->assertEquals(['cs', 'de', 'en', 'ru'], $factory->findAvailableLanguages($app), '', 0.0, 10, true);
+	}
+
+	public function dataLanguageExists() {
+		return [
+			[null, 'en', [], true],
+			[null, 'de', [], false],
+			[null, 'de', ['ru'], false],
+			[null, 'de', ['ru', 'de'], true],
+			['files', 'en', [], true],
+			['files', 'de', [], false],
+			['files', 'de', ['ru'], false],
+			['files', 'de', ['de', 'ru'], true],
+		];
+	}
+
+	/**
+	 * @dataProvider dataLanguageExists
+	 *
+	 * @param string|null $app
+	 * @param string $lang
+	 * @param string[] $availableLanguages
+	 * @param string $expected
+	 */
+	public function testLanguageExists($app, $lang, array $availableLanguages, $expected) {
+		$factory = $this->getFactory(['findAvailableLanguages']);
+		$factory->expects(($lang === 'en') ? $this->never() : $this->once())
+			->method('findAvailableLanguages')
+			->with($app)
+			->willReturn($availableLanguages);
+
+		$this->assertSame($expected, $factory->languageExists($app, $lang));
+	}
+
+	public function dataSetLanguageFromRequest() {
+		return [
+			// Language is available
+			[null, 'de', null, ['de'], 'de', 'de'],
+			[null, 'de,en', null, ['de'], 'de', 'de'],
+			[null, 'de-DE,en-US;q=0.8,en;q=0.6', null, ['de'], 'de', 'de'],
+			// Language is not available
+			[null, 'de', null, ['ru'], 'en', 'en'],
+			[null, 'de,en', null, ['ru', 'en'], 'en', 'en'],
+			[null, 'de-DE,en-US;q=0.8,en;q=0.6', null, ['ru', 'en'], 'en', 'en'],
+			// Language is available, but request language is set
+			[null, 'de', 'ru', ['de'], 'de', 'ru'],
+			[null, 'de,en', 'ru', ['de'], 'de', 'ru'],
+			[null, 'de-DE,en-US;q=0.8,en;q=0.6', 'ru', ['de'], 'de', 'ru'],
+		];
+	}
+
+	/**
+	 * @dataProvider dataSetLanguageFromRequest
+	 *
+	 * @param string|null $app
+	 * @param string $header
+	 * @param string|null $requestLanguage
+	 * @param string[] $availableLanguages
+	 * @param string $expected
+	 * @param string $expectedLang
+	 */
+	public function testSetLanguageFromRequest($app, $header, $requestLanguage, array $availableLanguages, $expected, $expectedLang) {
+		$factory = $this->getFactory(['findAvailableLanguages']);
+		$factory->expects($this->once())
+			->method('findAvailableLanguages')
+			->with($app)
+			->willReturn($availableLanguages);
+
+		$this->request->expects($this->once())
+			->method('getHeader')
+			->with('ACCEPT_LANGUAGE')
+			->willReturn($header);
+
+		if ($requestLanguage !== null) {
+			$this->invokePrivate($factory, 'requestLanguage', [$requestLanguage]);
+		}
+		$this->assertSame($expected, $factory->setLanguageFromRequest($app), 'Asserting returned language');
+		$this->assertSame($expectedLang, $this->invokePrivate($factory, 'requestLanguage'), 'Asserting stored language');
+	}
+
+	public function dataGetL10nFilesForApp() {
+		return [
+			[null, 'de', [\OC::$SERVERROOT . '/core/l10n/de.json']],
+			['core', 'ru', [\OC::$SERVERROOT . '/core/l10n/ru.json']],
+			['lib', 'ru', [\OC::$SERVERROOT . '/lib/l10n/ru.json']],
+			['settings', 'de', [\OC::$SERVERROOT . '/settings/l10n/de.json']],
+			['files', 'de', [\OC::$SERVERROOT . '/apps/files/l10n/de.json']],
+			['files', '_lang_never_exists_', []],
+			['_app_never_exists_', 'de', [\OC::$SERVERROOT . '/core/l10n/de.json']],
+		];
+	}
+
+	/**
+	 * @dataProvider dataGetL10nFilesForApp
+	 *
+	 * @param string|null $app
+	 * @param string $expected
+	 */
+	public function testGetL10nFilesForApp($app, $lang, $expected) {
+		$factory = $this->getFactory();
+		$this->assertSame($expected, $this->invokePrivate($factory, 'getL10nFilesForApp', [$app, $lang]));
+	}
+
+	public function dataFindL10NDir() {
+		return [
+			[null, \OC::$SERVERROOT . '/core/l10n/'],
+			['core', \OC::$SERVERROOT . '/core/l10n/'],
+			['lib', \OC::$SERVERROOT . '/lib/l10n/'],
+			['settings', \OC::$SERVERROOT . '/settings/l10n/'],
+			['files', \OC::$SERVERROOT . '/apps/files/l10n/'],
+			['_app_never_exists_', \OC::$SERVERROOT . '/core/l10n/'],
+		];
+	}
+
+	/**
+	 * @dataProvider dataFindL10NDir
+	 *
+	 * @param string|null $app
+	 * @param string $expected
+	 */
+	public function testFindL10NDir($app, $expected) {
+		$factory = $this->getFactory();
+		$this->assertSame($expected, $this->invokePrivate($factory, 'findL10nDir', [$app]));
+	}
+
+	public function dataCreatePluralFunction() {
+		return [
+			['nplurals=2; plural=(n != 1);', 0, 1],
+			['nplurals=2; plural=(n != 1);', 1, 0],
+			['nplurals=2; plural=(n != 1);', 2, 1],
+			['nplurals=3; plural=(n==1) ? 0 : (n>=2 && n<=4) ? 1 : 2;', 0, 2],
+			['nplurals=3; plural=(n==1) ? 0 : (n>=2 && n<=4) ? 1 : 2;', 1, 0],
+			['nplurals=3; plural=(n==1) ? 0 : (n>=2 && n<=4) ? 1 : 2;', 2, 1],
+			['nplurals=3; plural=(n==1) ? 0 : (n>=2 && n<=4) ? 1 : 2;', 3, 1],
+			['nplurals=3; plural=(n==1) ? 0 : (n>=2 && n<=4) ? 1 : 2;', 4, 1],
+			['nplurals=3; plural=(n==1) ? 0 : (n>=2 && n<=4) ? 1 : 2;', 5, 2],
+		];
+	}
+
+	/**
+	 * @dataProvider dataCreatePluralFunction
+	 *
+	 * @param string $function
+	 * @param int $count
+	 * @param int $expected
+	 */
+	public function testCreatePluralFunction($function, $count, $expected) {
+		$factory = $this->getFactory();
+		$fn = $factory->createPluralFunction($function);
+		$this->assertEquals($expected, $fn($count));
+	}
+}
diff --git a/tests/lib/l10n.php b/tests/lib/l10n/l10nlegacytest.php
similarity index 76%
rename from tests/lib/l10n.php
rename to tests/lib/l10n/l10nlegacytest.php
index d77548c5bf..ae84968e65 100644
--- a/tests/lib/l10n.php
+++ b/tests/lib/l10n/l10nlegacytest.php
@@ -6,11 +6,21 @@
  * See the COPYING-README file.
  */
 
-class Test_L10n extends \Test\TestCase {
+namespace Test\L10N;
+
+
+use OC_L10N;
+use DateTime;
+
+/**
+ * Class Test_L10n
+ * @group DB
+ */
+class L10nLegacyTest extends \Test\TestCase {
 
 	public function testGermanPluralTranslations() {
 		$l = new OC_L10N('test');
-		$transFile = OC::$SERVERROOT.'/tests/data/l10n/de.json';
+		$transFile = \OC::$SERVERROOT.'/tests/data/l10n/de.json';
 
 		$l->load($transFile);
 		$this->assertEquals('1 Datei', (string)$l->n('%n file', '%n files', 1));
@@ -19,7 +29,7 @@ class Test_L10n extends \Test\TestCase {
 
 	public function testRussianPluralTranslations() {
 		$l = new OC_L10N('test');
-		$transFile = OC::$SERVERROOT.'/tests/data/l10n/ru.json';
+		$transFile = \OC::$SERVERROOT.'/tests/data/l10n/ru.json';
 
 		$l->load($transFile);
 		$this->assertEquals('1 файл', (string)$l->n('%n file', '%n files', 1));
@@ -44,7 +54,7 @@ class Test_L10n extends \Test\TestCase {
 
 	public function testCzechPluralTranslations() {
 		$l = new OC_L10N('test');
-		$transFile = OC::$SERVERROOT.'/tests/data/l10n/cs.json';
+		$transFile = \OC::$SERVERROOT.'/tests/data/l10n/cs.json';
 
 		$l->load($transFile);
 		$this->assertEquals('1 okno', (string)$l->n('%n window', '%n windows', 1));
@@ -113,51 +123,8 @@ class Test_L10n extends \Test\TestCase {
 		$this->assertSame($expected, $l->l('firstday', 'firstday'));
 	}
 
-	/**
-	 * @dataProvider findLanguageData
-	 */
-	public function testFindLanguage($default, $preference, $expected) {
-		OC_User::setUserId(null);
-
-		$config = \OC::$server->getConfig();
-		if (is_null($default)) {
-			$config->deleteSystemValue('default_language');
-		} else {
-			$config->setSystemValue('default_language', $default);
-		}
-		$_SERVER['HTTP_ACCEPT_LANGUAGE'] = $preference;
-
-		$reflection = new \ReflectionClass('OC_L10N');
-		$prop = $reflection->getProperty('language');
-		$prop->setAccessible(1);
-		$prop->setValue('');
-		$prop->setAccessible(0);
-
-		$this->assertSame($expected, OC_L10N::findLanguage());
-	}
-
-	public function findLanguageData() {
-		return array(
-			// Exact match
-			array(null, 'de-DE,en;q=0.5', 'de_DE'),
-			array(null, 'de-DE,en-US;q=0.8,en;q=0.6', 'de_DE'),
-
-			// Best match
-			array(null, 'de-US,en;q=0.5', 'de'),
-			array(null, 'de-US,en-US;q=0.8,en;q=0.6', 'de'),
-
-			// The default_language config setting overrides browser preferences.
-			array('es_AR', 'de-DE,en;q=0.5', 'es_AR'),
-			array('es_AR', 'de-DE,en-US;q=0.8,en;q=0.6', 'es_AR'),
-
-			// Worst case default to english
-			array(null, '', 'en'),
-			array(null, null, 'en'),
-		);
-	}
-
 	public function testFactoryGetLanguageCode() {
-		$factory = new \OC\L10N\Factory();
+		$factory = new \OC\L10N\Factory($this->getMock('OCP\IConfig'), $this->getMock('OCP\IRequest'));
 		$l = $factory->get('lib', 'de');
 		$this->assertEquals('de', $l->getLanguageCode());
 	}
diff --git a/tests/lib/l10n/l10ntest.php b/tests/lib/l10n/l10ntest.php
new file mode 100644
index 0000000000..95546b4f78
--- /dev/null
+++ b/tests/lib/l10n/l10ntest.php
@@ -0,0 +1,162 @@
+<?php
+/**
+ * Copyright (c) 2016 Joas Schilling <nickvergessen@owncloud.com>
+ * This file is licensed under the Affero General Public License version 3 or
+ * later.
+ * See the COPYING-README file.
+ */
+
+namespace Test\L10N;
+
+
+use DateTime;
+use OC\L10N\Factory;
+use OC\L10N\L10N;
+use Test\TestCase;
+
+/**
+ * Class L10nTest
+ *
+ * @package Test\L10N
+ */
+class L10nTest extends TestCase {
+	/**
+	 * @return Factory
+	 */
+	protected function getFactory() {
+		/** @var \OCP\IConfig $config */
+		$config = $this->getMock('OCP\IConfig');
+		/** @var \OCP\IRequest $request */
+		$request = $this->getMock('OCP\IRequest');
+		return new Factory($config, $request);
+	}
+
+	public function testGermanPluralTranslations() {
+		$transFile = \OC::$SERVERROOT.'/tests/data/l10n/de.json';
+		$l = new L10N($this->getFactory(), 'test', 'de', [$transFile]);
+
+		$this->assertEquals('1 Datei', (string) $l->n('%n file', '%n files', 1));
+		$this->assertEquals('2 Dateien', (string) $l->n('%n file', '%n files', 2));
+	}
+
+	public function testRussianPluralTranslations() {
+		$transFile = \OC::$SERVERROOT.'/tests/data/l10n/ru.json';
+		$l = new L10N($this->getFactory(), 'test', 'ru', [$transFile]);
+
+		$this->assertEquals('1 файл', (string)$l->n('%n file', '%n files', 1));
+		$this->assertEquals('2 файла', (string)$l->n('%n file', '%n files', 2));
+		$this->assertEquals('6 файлов', (string)$l->n('%n file', '%n files', 6));
+		$this->assertEquals('21 файл', (string)$l->n('%n file', '%n files', 21));
+		$this->assertEquals('22 файла', (string)$l->n('%n file', '%n files', 22));
+		$this->assertEquals('26 файлов', (string)$l->n('%n file', '%n files', 26));
+
+		/*
+		  1 file	1 файл	1 папка
+		2-4 files	2-4 файла	2-4 папки
+		5-20 files	5-20 файлов	5-20 папок
+		21 files	21 файл	21 папка
+		22-24 files	22-24 файла	22-24 папки
+		25-30 files	25-30 файлов	25-30 папок
+		etc
+		100 files	100 файлов,	100 папок
+		1000 files	1000 файлов	1000 папок
+		*/
+	}
+
+	public function testCzechPluralTranslations() {
+		$transFile = \OC::$SERVERROOT.'/tests/data/l10n/cs.json';
+		$l = new L10N($this->getFactory(), 'test', 'cs', [$transFile]);
+
+		$this->assertEquals('1 okno', (string)$l->n('%n window', '%n windows', 1));
+		$this->assertEquals('2 okna', (string)$l->n('%n window', '%n windows', 2));
+		$this->assertEquals('5 oken', (string)$l->n('%n window', '%n windows', 5));
+	}
+
+	public function localizationData() {
+		return array(
+			// timestamp as string
+			array('February 13, 2009 at 11:31:30 PM GMT+0', 'en', 'datetime', '1234567890'),
+			array('13. Februar 2009 um 23:31:30 GMT+0', 'de', 'datetime', '1234567890'),
+			array('February 13, 2009', 'en', 'date', '1234567890'),
+			array('13. Februar 2009', 'de', 'date', '1234567890'),
+			array('11:31:30 PM GMT+0', 'en', 'time', '1234567890'),
+			array('23:31:30 GMT+0', 'de', 'time', '1234567890'),
+
+			// timestamp as int
+			array('February 13, 2009 at 11:31:30 PM GMT+0', 'en', 'datetime', 1234567890),
+			array('13. Februar 2009 um 23:31:30 GMT+0', 'de', 'datetime', 1234567890),
+			array('February 13, 2009', 'en', 'date', 1234567890),
+			array('13. Februar 2009', 'de', 'date', 1234567890),
+			array('11:31:30 PM GMT+0', 'en', 'time', 1234567890),
+			array('23:31:30 GMT+0', 'de', 'time', 1234567890),
+
+			// DateTime object
+			array('February 13, 2009 at 11:31:30 PM GMT+0', 'en', 'datetime', new DateTime('@1234567890')),
+			array('13. Februar 2009 um 23:31:30 GMT+0', 'de', 'datetime', new DateTime('@1234567890')),
+			array('February 13, 2009', 'en', 'date', new DateTime('@1234567890')),
+			array('13. Februar 2009', 'de', 'date', new DateTime('@1234567890')),
+			array('11:31:30 PM GMT+0', 'en', 'time', new DateTime('@1234567890')),
+			array('23:31:30 GMT+0', 'de', 'time', new DateTime('@1234567890')),
+
+			// en_GB
+			array('13 February 2009 at 23:31:30 GMT+0', 'en_GB', 'datetime', new DateTime('@1234567890')),
+			array('13 February 2009', 'en_GB', 'date', new DateTime('@1234567890')),
+			array('23:31:30 GMT+0', 'en_GB', 'time', new DateTime('@1234567890')),
+			array('13 February 2009 at 23:31:30 GMT+0', 'en-GB', 'datetime', new DateTime('@1234567890')),
+			array('13 February 2009', 'en-GB', 'date', new DateTime('@1234567890')),
+			array('23:31:30 GMT+0', 'en-GB', 'time', new DateTime('@1234567890')),
+		);
+	}
+
+	/**
+	 * @dataProvider localizationData
+	 */
+	public function testNumericStringLocalization($expectedDate, $lang, $type, $value) {
+		$l = new L10N($this->getFactory(), 'test', $lang, []);
+		$this->assertSame($expectedDate, $l->l($type, $value));
+	}
+
+	public function firstDayData() {
+		return array(
+			array(1, 'de'),
+			array(0, 'en'),
+		);
+	}
+
+	/**
+	 * @dataProvider firstDayData
+	 * @param $expected
+	 * @param $lang
+	 */
+	public function testFirstWeekDay($expected, $lang) {
+		$l = new L10N($this->getFactory(), 'test', $lang, []);
+		$this->assertSame($expected, $l->l('firstday', 'firstday'));
+	}
+
+	public function jsDateData() {
+		return array(
+			array('dd.MM.yy', 'de'),
+			array('M/d/yy', 'en'),
+		);
+	}
+
+	/**
+	 * @dataProvider jsDateData
+	 * @param $expected
+	 * @param $lang
+	 */
+	public function testJSDate($expected, $lang) {
+		$l = new L10N($this->getFactory(), 'test', $lang, []);
+		$this->assertSame($expected, $l->l('jsdate', 'jsdate'));
+	}
+
+	public function testFactoryGetLanguageCode() {
+		$l = $this->getFactory()->get('lib', 'de');
+		$this->assertEquals('de', $l->getLanguageCode());
+	}
+
+	public function testServiceGetLanguageCode() {
+		$l = \OC::$server->getL10N('lib', 'de');
+		$this->assertEquals('de', $l->getLanguageCode());
+	}
+}
diff --git a/tests/lib/testcase.php b/tests/lib/testcase.php
index 38d5cf4932..008b96b341 100644
--- a/tests/lib/testcase.php
+++ b/tests/lib/testcase.php
@@ -36,6 +36,46 @@ abstract class TestCase extends \PHPUnit_Framework_TestCase {
 	static protected $realDatabase = null;
 	static private $wasDatabaseAllowed = false;
 
+	/** @var array */
+	protected $services = [];
+
+	/**
+	 * @param string $name
+	 * @param mixed $newService
+	 * @return bool
+	 */
+	public function overwriteService($name, $newService) {
+		if (isset($this->services[$name])) {
+			return false;
+		}
+
+		$this->services[$name] = \OC::$server->query($name);
+		\OC::$server->registerService($name, function () use ($newService) {
+			return $newService;
+		});
+
+		return true;
+	}
+
+	/**
+	 * @param string $name
+	 * @return bool
+	 */
+	public function restoreService($name) {
+		if (isset($this->services[$name])) {
+			$oldService = $this->services[$name];
+			\OC::$server->registerService($name, function () use ($oldService) {
+				return $oldService;
+			});
+
+
+			unset($this->services[$name]);
+			return true;
+		}
+
+		return false;
+	}
+
 	protected function getTestTraits() {
 		$traits = [];
 		$class = $this;