Носитель языка. Иногда на жаргоне, но обязательно в контексте - натив (с ударением на и).

Носитель языка - literally 'language carrier". This term could originate in linguistics (I'm not sure though) , judging by its literal meaning... or at least I first met in the context of linguistics. It also became widely used in the context of language education: advertisments of language courses with "занятия ведут носители языка" are familiar to everybody since 90s. But if I speak about my friend, I'd avoid this term, unless I speak in the context of linguistics: sounds too much as a _term_. You may reword it as "французский — её родной язык" (French is her mother tongue), "её родной язык - французский" (her mother tongue is French) etc. Personally I would not use it is speaking about myself too, in a résumé or job application... and I wouldn't say so about my language teacher (or any specific person in the context of education)... But I'm sure many people would use it. It is matter of taste.

Native speaker Носитель языка. Носитель (+Genitive case) французского языка. Носитель русского языка.

Native speaker - носитель языка ( человек, для которого этот язык является родным )someone who has spoken a particular language since they were a baby, rather than having learnt it as a child or adult.

Человек, для которого Русский - это родной язык(человек, родной язык которого, Русский).