I think you're trying to say "to put somebody off learning a language". For example, "I was really keen on learning English but my friend put me off when she told me it would take many years and lots of money".

No. You "scare off" a person, not their wish. So you could say, "He wished to learn a foreign language but the grammar scared him off." Or you could say "the grammar scared him out of his wish to learn a foreign language."