The Google Glass device probably uses the same voice recognition as Android. Android is not in beta anymore, yet its voice recognition fails pretty bad on anything other than English. Google Now is almost entirely useless unless your device is set to US English.
I get that they can't exactly make everything work perfectly for everyone. But most of the planet is not american. They want to interact with technology on their own terms, in their own language. Google is long past the point at which it can make excuses now. While breaking new grounds with stuff like Google Glass is very cool, so is offering useful voice recognition to most of the planet.