Don't assume languages are 2 letter codes.

Also, note that this method never worked. Locale
settings were stored with underscores (like Locale.toString)
but matched against AssetManager.getLocales() which
returned language-tag like output.

bug: 10090157

(cherry picked from commit fd138cd8)

Change-Id: Ifc81ac902c297387dba8c40aba0656e18af57c86