This allows us to use this new filter to translate strings from a given array of translations, where every translation is indexed by its ISO 639 code. A new configuration option ('language' -> 'priorities') is available too to control the alternative languages that can be used instead of a given language, when the latter is not found. The filter returns null when no suitable translation is found, so that it can be combined with "default()" to set a default translation for a given string.

Therefore, it should be accessed using self, not $this.

bugfix: $langPath won't be defined if an exception is thrown by the method where we get its value from.

Add a couple of methods to perform translations with PHP's native gettext implementation, and start using them.

Use \SimpleSAML\Logger in the new Localization class, and fix general Exception being called from a namespace.

These two methods are equivalent to gettext/gettext's __() and n__(), but using strtr() instead of vsprintf(), so that the placeholders can be names instead of printf() format strings.

This makes instanciating the Translate/Template-class unnecessary.

For #455

For #455