UI and & subtitles localisation for additional languages. At least Spanish, Russian and Brazilian Portuguese. It doesn't need voice acting.

This is one of the biggest MMOs in the world but the lack of some languages is baffling.
Guild Wars 2 has Spanish, ESO added Russian last year, and is adding Chinese later this year.
BDO has Turkish servers. Even Swords of Legends by Gameforge got a Russian translation and that is DOA.