That would be a fairly significant change - particularly the interface in a story entry as that would need to be changed to allow entering of a language as well as a speaker. Story entries are stored in the Fantasy Grounds formattedtextcontrol control and there is very little that can be done programatically with information that is stored in that control. I can't think of a way to store language information in a story entry and make it available to the languages extension.
It has been mentioned in the past about having a way of setting the current language for all chat entries, so that everything that would be shown as a "chat" entry (in the speech bubble) would use the language font. I've added this to the future development ideas in post #2, don't don't expect anything soon...