国 + 人【guó + rén】

A nationality is the country plus 人. There is nothing else to learn and no irregular forms.

中国人, 英国人, 美国人, 法国人, 日本人, 西班牙人.

The language is 语 or 文

汉语 and 中文 both mean Chinese, 英语 and 英文 both mean English. 语 leans towards the spoken language and 文 towards the written one, but in ordinary use they are interchangeable.

Asking

哪国人, not shén me什幺guó rén国人. 哪 asks you to pick from a set, and countries are a set.

To ask about a region instead, 你是哪里人 covers where in a country someone is from.

外国人 and 留学生

外国人 is a foreigner, 留学生 a student from abroad. Both are plain descriptions.

The country name also works as a modifier

中国菜, 英国电影, 法国红酒 – no 的 needed.