"So we're agreed, both sides of the argument are valid. "

It depends what "arguement" you are having. Frankly, I thought we were having a discussion. If it were an argument, I would have said something about nasty about your mother and her relationship with the local football team!!   

If you are asking me if there should be an "official" language, the answer is no - there is no valid reason to have one.

If you are asking me if people should learn the popular language of the country in which they live, I agree that all attempts should be made to learn it.