Fix region langs not generating the correct values folder.

[asier2]

Format lang-region code for values folders as required by Android. ('es-es' -> 'es-rES')

https://developer.android.com/guide/topics/resources/providing-resources#AlternativeResources:

The language is defined by a two-letter ISO 639-1 language code, optionally followed by a two-letter ISO 3166-1-alpha-2 region code (preceded by lowercase r).

The codes are not case-sensitive. The r prefix is used to distinguish the region portion. You can't specify a region alone.