A student keeps using a native language while asking questions in the class when the course is taught in English

If you want a non-confrontation approach, simply repeat the question in English before answering it.

Hearing the translation may help the student in question see how to phrase their questions in English. It also give a polite hint that the question should have been asked in English.

My suggestion is that you either let it go, if everyone understands what the student has said, or that you explore the situation with the student during office hours. Perhaps it is just easier for this student to say subtle things as needed in his/her native language than in English. It is fine if you make an explicit request, but be prepared to yield if the student has good reasons.

It is fine that you continue to reply in English, but it wouldn't be fine if you somehow embarrass the student about language use.

Be thankful, actually, that the student is willing to participate and ask questions no matter the language. Too many students leave questions unasked when other students have the same questions but also don't ask them. That makes education less efficient.

If this is the US, by the way, we are a multilingual country already, in spite of what some "nativists" want you to believe and want to impose on you and me.

Of course the answer would be different if this were a language course, rather than statistics.

I am assuming that learning how to discuss statistics in English is not specifically part of the course syllabus. If it is, you should simply tell the student to speak English.

If the students' questions are otherwise good, assume the best - that the student simply does not feel confident asking in English.

I have had similar situations in courses before. My approach has been to tell the students that I prefer that they ask questions in the language the course is given, but if they cannot, just ask in another language I can understand, and I will translate the question and answer in English.