国 + 人【guó + rén】

A nationality is the country name plus 人: 中国人, 英国人, 美国人, 法国人, 西班牙人. There are no irregular forms.

Asking

哪国人 asks which country. 哪 asks you to pick from a set, so 什么 doesn't fit here.

• × 你是什么国人？ → 你是哪国人？

你是哪里人 asks where someone comes from, usually their home town or region.

The language takes 语 or 文

A language usually swaps 国 for 语 or 文: 英国 → 英语 / 英文, 法国 → 法语 / 法文. A country name without 国 keeps the whole name: 西班牙语. 语 leans towards the spoken language and 文 towards the written one, but in everyday use they are interchangeable.

Chinese itself is 汉语 or 中文.

• × 中国语 → 汉语 / 中文

The country name also goes straight in front of a noun, without 的: 中国菜, 英国电影, 法国红酒.

外国人 is a foreigner and 留学生 an international student.