Don't use substring matching on locales.

We can't assume that all languages will be 2 chars in length.
Language matching will need to parse the language subtag from
the locale, else we might end up matching a languages like
"fi" (finnish) to "fil" (filipino).

bug: 10090157
Change-Id: Ie394d9fa5e45e49a6d90bb107783de7a9e17b766