Isn't it Vietnamese only?

Nope. I'd have to reinstall it to check exactly which languages are included, but English is definitely one of the ones included in the international release available on Gamersgate (I think French and German might be as well). I played with Vietnamese audio and English subtitles, but I remember I could have chosen English audio.

EDIT: English, French, and Vietnamese. I did remember wrong though, apparently can't choose a different languages for subtitles and audio (which is a shame, I do like having the original language spoken and reading in something I can understand).

Cool, thanks.
I thought someone said, it's only in vietnamese when it was discussed here some time ago. Good to hear I was wrong, I think I will pick it up somewhere in the future.

I believe it'll pick the language you chose in the installer the first time you launch it (English or French), or the language of your system. But if for whatever reason it isn't in English (it was in Vietnamese when I installed it now, I probably had managed to change the language some time before I decided to uninstall it, and the setting remained despite the game being uninstalled), the steps to change language are:

(If it's in French)
Réglages
Général
Click where it says "Français" a couple times until it's in English.

(If Vietnamese)
Tuy Chinh
Thiet lap tro choi
Click where it says "Tieng Viet" until it's in English
(I ignored the various marks used because it's a pain to copy them using charmap, but the basic letters should guide your way)

Then apply and go back to the main menu.