Why does tongo speak french?

There seems to be a misunderstanding. "Tongo" is not a country or a language. It's likely you're thinking of "Togo", a country in West Africa.

Togo does not speak French as its primary language. While French is an official language, the most spoken language in Togo is Twi, followed by Ewe, Mina, and French.

It's important to be precise with names and terms to avoid confusion.