I am talking about singleplayer maps and not multiplayer maps, apologies for not making that clear in my last post. From what I have tested using the Spanish version Scrapy provided, I was able to get the Spanish campaign to load without crashing the game by taking its campaign maps, its...
Yes, you will need the campaign map files of the game in the language you wish to play in. Otherwise, you will need to install Halo 2 from a DVD or ISO that is in the language you are looking for.