Two or three letter country codes?

[aaronstc]

I'm trying to set default subtitle language to english and VLC says to use country codes. Problem is I have no idea what the codes are. I've tried US, USA, EN, ENG, UK. None of those seemed to work.

[Placio74]

Three letter ISO 639-2.

I'm used in VLC settings and work for MKV and OGM.
(Of course if correct language is defined in container.)

I'm change default track in MKV (used MKVtoolnix) - work in VLC.

[angooolak]

I use a free web-based online tool that provides with an interface to find country, dialing code and 2-Letter code of each country. It features auto-complete search, so you can find the countries and codes as you type.

or you can just select the country and see the 2-Letter code.
http://www.etyn.com/tools/country-codes

cheers.