To what extent do people who want to speak French at job fairs in foreign companies require French, and what French grade certificate should they get?

It depends on what position you are applying for. If you are a translator, you must have at least TEM-8, preferably a translation certificate. If not, you can consider studying abroad to do the corresponding major, and some may need work experience. If French is only an auxiliary language, the requirements may be lowered. It's hard to say. The foreign companies my classmates are looking for usually see French university diplomas. It depends on the requirements of the employer.

There must be a level four. At least I don't think the recruitment threshold is lower than this. Tcf is used abroad, but it is basically useless at home.