Click the Language Maintenance button and choose "Add Missing Translations"
(skip the normal step of importing...)
Run the Synchronize Terminology process.
Log out and log in as Super User with your new language. Even though most everything will be in English because you have not imported the translations, you will be using the translation tables.
I tried this process with three langues (Albanian, English [UK], and Czeck). Only the Turkish Language failed.
I've also tried on fresh iDempiere installation. What should I do?