I've always liked this picture http://www.lingholic.com/wp-content/uploads/2014/05/Hard-Languages-To-Learn.png

As for other Romance languages, don't you constantly forget if you actually learned a word or a grammar rule or you simply invented it yourself by analogy with the Spanish one?

As for Russian, it is not so difficult. You should simply put some effort to understand its structure and never use the colloquial method learning it. I know people who had a great progress in Russian quickly enough.

i think turkish is hard for you to learn. Totaly different grammar rules exist .

You are definitely right. Portuguese is the easiest language to learn for Spaniards (hispanohablantes) followed by Italian and French. When it comes to Germanic languages English is the easiest because it has a lot of latin words. According to language experts Chinese, Japanese, Korean and Arabic are the most difficult languages in th world . You need to spend 2200 class hours learning one of the languages to be fluent. Russian which is a Slavic language is more difficult than Germanic languages but much easier than Arabic. You need 1200 class hours to achive proficiency. 

@mapa1384 - It's hard to take you as a serious learner of Russian or Arabic, since you haven't even put them on your language list. My advice is to first add them; if you can't bring yourself to do that little step, there is no need for you to worry about attempting them at all.

Hello ,, Me as Arabic still very dificult to me to learn formal Arabic it is one of the hardest language ever im not saying im bad in arabic i'm good in arbaic ,, may i can help you ..