Hi Mariam! For me When I'm trying to speak- write in English, I'm really at a loss to choose words to explain my feelings and my point, etc.

i am french language teacher , i have problem with reading vowels because of languages confusion

For me it would have to be the pronunciation and different phonetic aspects of the language, its seemingly arbitrary way on how you pronounce certain words one way and some others in a totally different manner even though they share the same vowels and consonants.

Other than that I think English is one of the easiest languages to learn. 

Slangs and expressins are alot and diffucult to memorize them i.e. you must be in contact with an English native speaker to get aware of the application of a particular slang.