Oh, that's no fun. No fun at all. :)

Good Question. suppose you have to introduce yourself to other person who know other language or or you find your self among those people who do not know your mother tongue is such a situation what would you do?

can't choose which one

I think it's also important to look at the practicalities of this as well. Dialects naturally emerge even within the same country. Language is always changing. In order to keep it static, you'd need someway of ensuring that everyone is communicating with lots of different people. Increasing globalization may make this more possible in the future, but there's no chance in the present.

i guess that will boring.it will be no cultures no traditions to speak about, to be proud of or to learn about.being human mean being curious that what is kkeping us alive.Curiosity, what is going to happen tomorrow, next week... etc that what is giving us hope to stand another day. for me if all the world has been speaking the same language i will lost my pleasure of discovering new nation and new people.