This is not really supported but possible by changing the Configuration object's "locale" field [Google Groups Post]
Configuration c = new Configuration(getResources().getConfiguration());
c.locale = Locale.GERMAN;
getResources().updateConfiguration(c, getResources().getDisplayMetrics());
Note that this alone will only effect future strings, not ones already displayed on the screen. You'd want to do this from a different activity than your main one, then finish your main one and restart it.
This is hacky. See Post from Hackborn
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