Chyba nie wiesz jak strasznie chce się nauczyć francuskiego.

[altynek]

English Translation

You don’t know how bad I want to learn how to speak French.

“I want” should be “he wants”?

[waxapax]

you’re right, it’s a mistake. Report it please.

Btw, I think it should be badly, so there is a mistake in both sentence and translation

[nuxenolith]

English Translation

You don’t know how bad he wants to learn how to speak French.

“How bad” is a more colloquial form of “how badly”…Americans particularly love using adjective forms when traditional grammar rules call for an adverb. For example, “How was the movie?” “Real good!”