A time ago I translated the whole thing to Spanish for my own use, since I'm from Argentina and we talk that language.
And I think it's time to share it with whoever wants to have it done and is too lazy to do it for himself :P

WARNING: I recommend creating a backup of the existing "Cube\data\menus.cfg", since if something doesn't work, or you want to go back to the original, it's not possible if you overwrited the original unless you reinstall the game.

Note: This is for the release of 29-08-2005 of Cube.

Instalation: place the downloaded "menus.cfg" in the "Cube\data\" folder and overwrite the original.

Enjoy!