I think Mandarin would be more difficult!

Hungarian and Russian

I've heard - Russian language the most difficult to learn.

Bonjour, The best way to answer your question is to try...

French is quite difficult to learn because of the grammar, many rules and verbs! The prononciation is different than reading .There are many silent letters so it can be hard for foreign people to pronunce right! I don't know which language is the most difficult because it depends on people, motivation and how fast your learn things! Russian can be difficult because it's different :) Some people says Spanish/Italian/Portuguese are easier than French ! Before starting to learn a language, you need to know why do you want to learn this language! and you have to learn the culture as well! That's very important :) it makes your learning more interesting!