[BUGFIX] Using XLIFF v.1.2 breaks ll-XML conversion on Pootle

Change-Id: Ie0e3787d681b4927f8d7fdd6d775a254e6a4a7fc
Reviewed-on: https://review.typo3.org/28551
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers