[RealJames]

1) Is Japanese a hard language to learn from someone who live in Europe?

Spoken Japanese is relatively simple. Honestly quite easy.
Written Japanese is so hard because of the two thousand kanji you gotta learn to read the local paper. The Hiragana and Katakana characters are dead simple and luckily phonetic, unlike French or English.

2) What is the average time to learn Japanese to have the "level" to speak "easily" in nearly all situations (like on the forum or in conversation)

It took me about a year, living in Japan, using it for about 1 or 2 hours a day. But that's to be able to hold a conversation in most topics.

3) What about the pronounciation of this language?

So easy, like I said it's phonetic also with it's writing so you can even learn words by listening and then looking up.

4) About the difficulty, how do you compare the French and the Japanese language?

French has SO many exceptions and it also has rules which cant be learned (male female, conjugation exceptions etc). Japanese is minimalistic in comparison, the most difficult thing is to learn how to say more with less words haha.

PS. I also speak French English and Japanese