There are three places you can change locale and they have a priority order assigned to them. I forget exactly how it works, but your blog has a locale, your user has a locale, and each post has a locale. I think that's the reverse of the order it goes by, so if you change your blog but not user then the user locale wins. If you change the post locale then it always wins.
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There are three places you can change locale and they have a priority order assigned to them. I forget exactly how it works, but your blog has a locale, your user has a locale, and each post has a locale. I think that's the reverse of the order it goes by, so if you change your blog but not user then the user locale wins. If you change the post locale then it always wins.