WordPress is now used all other the world in dozens of languages.
The reason is that from the start wordpress used a very nice translation scheme.
WordPress default theme is hence very easily translated into any language through the usage of mo and po files.
However for a reason I don't understand, the default theme is not fully gettexted so that even if you do want to have the theme fully in another language, it's not possible.
Why not fully translate the default theme? Most new themes will follow and all the appropriate string will be included in the main mo file.
It's not a big amount of work, but will make our life a lot easier!