fix: filter lang map

[arzola]

Problem

• Transifex translations are not working as expected, we introduced a change chore: add transifex config, bump version #430 to try to setup automated github sync with transifex but we are dealing with some issues regarding duplicate translation resources and missing translations.

Translation files filenames

** Before **

languages/es_ES.mo

Now

languages/pressbooks-aldine-es_ES.mo

Solution

• Revert the translation prefix change because the old translations on this plugin are not using a prefix like pressbooks does, you can look at previous commits files doesn't contains a prefix 7e6ef6b

** After this change **

languages/es_ES.mo

[fdalcin]

LGTM