Change locale names to follow Rails i18n.

Think the locales are maintained now on locale app but do a pull request anyway.

Changed filenames of 3 locales so they follow [Rails i18n](https://github.com/svenfuchs/rails-i18n/tree/master/rails/locale) in an ISO style to avoid fallback confusion. This is similar to 9d7a60d so I did not change locale for Czech.