Report What's the most challenging about learning a foreign language? in Language Learning Posted July 21, 2016 Grammar. Absolutely. My one true bane. Whenever I speak in other languages, I try to be very cautious with the conjugations of words. But after all is said and done, I then realize the few (or more) grammatical errors I just made. It makes me think, "shoot! I shouldn't have said that! Think before you speak!" Unfortunately, I never do, haha. As Bruce Lee once said: "Don't think. Feel." Which is basically the level I want to be in all the languages I learn.