mother tongue
native language , auch: native tongue

They can't be serious about not using a native language.

Some did not have a word for it in their native language.

S1 and S2 might not speak the same native language.

Smith said something that must have been in his native language.

Several other books in his native language have also been published.

And how is it that we hear, each of us in his own native language?

The measure of a person's total control over his native language.

The young generation in general does not speak their native language.

However, this native language will still be present in the way they both speak and write.

Well, stick to Common or whatever your native language is.