To add community translations to a retro ROM, download a patch file, find a patch tool and use it to add a patch to the Retro ROM. Details here.

Soul Eater: Medusa no Inbou, a DS spinoff game based on the anime, has gotten a full English translation that keeps faithful to the subs.

The first Ni no Kuni game on Nintendo DS has gotten a full fan translation, including the full 352-page tome that came with the game.