[BUGFIX] Fixes wrong locale in XLIFF models
If a translation is requested but no (exact) match is found,
a different locale may take effect (e.g. en instead of en_UK).
The XLIFF model created will refer to the en XLIFF file, but
claim it's locale is en_UK. This leads to further problems
with translations (like missing labels if no target elements
are present in XLIFF files).
This change fixes that…