their native + language | tongue – English Grammar Profiler

‘your native language or tongue’ is B2 in the English Vocabulary Profile with the meaning: ‘the first language you learn.’  For example:

Now, they speak English but it‘s not their native language, 

they‘d rather not speak English.

TED

A collocate search for _APPGE native language|tongue in COCA:

1 LANGUAGE 566
2 THEIR 412

3 TONGUE 3004 ENGLISH 80 5 SPEAK 53 6 SPEAKING 28 7 SPANISH 23 8 SPOKE 20 9 SPEAKS 16

10 LEARN 11