To get around what is really a bug in Doulos, the OO Graphite language mapping takes 2 letter language codes and matches any 3 letter code in the font that has the same 2 letter prefix.
This is too ambiguous (e.g. which should vi match? via, vie, vit). Instead vi should match vi and a bug be raised on Doulos SIL to get vi as a language in there (since vi is the ISO639 code).