There isn't an API to change the current iPhone system-wide language settings from
within an application. In general, this behavior is discouraged, since it would
be confusing from a user's point of view.
If you need to load resources for a different language, based on, perhaps, an in-app
setting, you can do this in your application by using NSBundle APIs like
NSBundle:pathForResource:ofType:inDirectory:forLocalization to get the relative path
to a particular language resource lproj folder in the bundle, and then loading these
resources manually. See the following docs for more details on this: