Localization (for the most part) is an extremely easy way to get Cocoa apps to support multiple languages on Mac OS X. I've spent the past two days making Wallet 2 localizable, and it has been fun! Lots of users are willing to help and port Wallet 2 to their native language. I only have to change a few strings, and everything is automatically built in. However...

Multiple nibs. This part REALLY gets on my nerves, because now I have to update every version of the NIB manually every time I want to make an interface change. Or, I'll be forced to make these changes by code. Seriously though, Apple needs a nice way for interfaces to stay-in-sync with multiple languages. I really do dread lots of languages in the future, because I'm bound to make an error sooner or later because of a very simple language change. Whoops, disconnected an outlet and broke Wallet in Spanish! Damnit.

Overall, it's great. Wallet 2.0.2 (in the works) will support German, with more languages to come in 2.1 and so on.

If you're interested in helping translate to a language, see this forum post.