introduce new function to force a language

lib/private/l10n.php

@@ -418,6 +418,14 @@ class OC_L10N implements \OCP\IL10N {
 		return $text[$lang];
 	}
 
+	/**
+	 * The given language is forced to be used while executing the current request
+	 * @param string $lang
+	 */
+	public static function forceLanguage($lang) {
+		self::$language = $lang;
+	}
+
 	/**
 	 * @brief find the best language
 	 * @param array|string $app details below