Mother Tongue is mother language, and it is speaker's native language. You can treat it as the language that the speaker first learnt since birth (from his/her mother, usually).

It's only "mother tongue". "Mother language" is laughably poor English (so is "wanna"). 雲小泉 is right in saying that a mother tongue is what YOU speak, not necessarily what is spoken in your country. Your proper question is: 'If I say "mother tongue" to refer to the language spoken in my country, is that wrong?"

"Mother language" is not correct! "Mother tongue" refers to YOUR mother tongue or the mother tongue of the people. It is not necessarily the language of a nation! There's a big difference.

Mother tongue is correct. I've never seen "mother language" used in English.

@Robert: on MSN you clarify my doubt(from your point of view), so... DON'T DISAPPEAR!!