get_regions('es') doesn't get any Spanish locale

[jsocol]

Currently, we have support for over-specifying a locale, e.g.:

product_details.get_regions('fr-FR')

will return the same data as get_regions('fr').

But we don't support underspecifying a locale, for example:

product_Details.get_regions('es')

will return English, because that's the fallback.

The accept-languages spec says we can return anything. I'm guessing es-ES would probably be best in that case, but

• I don't actually know it's the best.
• This isn't accept-language, we don't have to adhere exactly.

A motivating example of this is SUMO, which has a single es locale, instead of the various es-* that product_details has.

[fwenzel]

This heuristic would also be kind of expensive (parse file list, search through it for a certain pattern, so we should make sure we don't run it too often.

Another place to fix it at would be on the data side. Symlink in SVN from es -> es-ES? I do fear that if we pick any then we'll run into edge cases where people do not just want "any" flavor of their language :-/