I think that as global communication improves the language barrier will gradually disappear. This is not to say that there won't be different languages (at least for a good long while), just that everyone will be able to understand each other. Probably a few of the more obscure languages will die out, a few others will be kept deliberately alive although their speakers will have fluency in the "mainstream" languages as well. Some words will disappear, others will migrate between languages. Techniques for teaching language will improve so that the remaining languages will be spoken and understood by everyone. Perhaps eventually these languages will become (effectively) a single language that everyone speaks.
Then we'll make contact with aliens and have a language barrier again just as we've forgotten all our techniques for effectively living with it.