There is in-game support for adding translations, sort of. You just drop files into a folder and there you go. (This is in fact how our Russian and Korean translations turned up, fans had started working on them on their own, and then started emailing their work to us).

The only thing that requires a lot of heavy lifting is if that language requires a previously unsupported font (like a new Asian language), or if the new language has problems fitting in the User Interface.

As I said in the article, I would not consider fan translations a replacement for professionals so much as a supplement, although I guess this depends on the needs of your app/game. In my case we had a big story-based RPG with 45,000+ words, which is not a trivial exercise and there's all sorts of opportunities for it to go off the rails in ways that kill the sparkle (inconsistent grammar, poor or erroneous characterization, horrible translations of jokes, etc). Fans can and do produce great work, but you can't assume that's what you'll receive.

For languages you're really interested in targeting (for us our top priority was German) you don't want to roll the dice on that. But for "like to have" languages it's not a bad idea.