After submitting our app into AppStore in Canada, we found that the Language is "Chinese". In fact, our app is in English at the same time and its description is all in English.
The only place which I think may concern is the "Localization native development region" info.plist entry. But I'm not sure whether changing this entry to en_US will help display the right language in AppStore.
related question: AppStore language description and "Localization native development region"
But I can't catch the answer...