In a interview with Hourrafoot, when asked:
Yohan, comme Ludovic Obraniak, quelle autre nationalité pourrais-tu demander si Laurent Blanc ne te sélectionne pas en équipe de France après la Coupe du Monde ?
Ah bon, c’est fait, c’est Laurent Blanc ? Je pourrais jouer pour le Viêt-Nam, ma grand-mère est vietnamienne ! Mais ça fait un peu loin.
I can't read French but it can be translated as something like this:
Yohan, as Ludovic Obraniak (a French player who chose to play for Poland), what other nationality would you have if Laurent Blanc doesn't select you for France national team after the World Cup?
Oh, it's done, Laurent Blanc? I could play for Vietnam, my grandmother is Vietnamese! But it's a bit far.
Yes, it's an interesting story there. However, he has made his debut for France national team in August 2010 and will not be available for Vietnam any more. There are a lot of young Vietnamese players playing in France, Germany and Czech Republic. Just hope they will become good ones and play for Vietnam someday.