Not respecting LANGUAGE variable properly (default language).

Consider the following extract from localectl's output:

System Locale:

LANG=en_US.UTF-8

LANGUAGE=en_US:C:de_DE

LC_MESSAGES=en_US.UTF-8

With this, all parts of xfce should actually show English language. Garcon (and xfce4-settings) do not. I assume the two compare the LANGUAGE variable against xfce's LINGUAS list and choose the first match. Many applications do not explicitly alias their default language with its respective name (e.g., en_US). At least "C" should still be respected (as, e.g., xfce4-panel does).