Also its worth to familiarize oneself with String Resources section of the Resource Programming Guide.
Regional conventions is quite an interesting topic by itself but I won’t go into big detail about that.
They describe conventions based on cultural, historical and lingual context.
People expect those conventions to be followed and may be seriously confused or even seduced if not.
(I’ll cover this in more details below later, note that there are issues about that in i OS9).
So, NSBundle is usually the one to ask for language.
Say, there’s a girl Jane, who likes [ to get with her.
If you talk to Jane’s sister, she’ll tell you about Jane’s priorities in general, that’s NSLocale.
If you talk to your buddy - he’ll advice you to weight upon something you’re good at among what Jane likes, that’s NSBundle.