When you add a directory to a data project with hidden files in it, the list of filtered files appears. Here in the Type column, the file types appear untranslated, despite being translated in the po files.

This is because the list of filtered file types is part of a string array, and the strings are marked for translation with the N_ macro. In such cases, you must call gettext() at the place where the array items are actually used. This does not happen in this case.

See also: http://www.gnu.org/software/gettext/manual/gettext.html#Special-cases