It doesn't help that English is one of the harder languages to learn in general
English is the easiest language to learn! Try german, russian or chinese if you want something hard to learn...
It's funny that you chose three of the four non-English languages I've studied somewhat (the fourth was the one I studied the longest, which is French).
Grammatically, Mandarin Chinese didn't appear too difficult - no conjugating verbs, you'd just add an extra character to denote something was in the past rather than the present. Of course, speaking it was a different story, as each syllable had its own intonation (whether it was high, rising, falling or down and up, or something like that - I've forgotten the specifics). And characters instead of an alphabet make it harder to pick up when reading some unknown text - you can't really sound something out as one can in the other languages.