The comment that ragtag3333/Linguist made on The Hardest Part About Arabic post got me thinking about some of the difficulties that Arabic speakers have with English. Now I've never had to learn English and am not a native speaker of Arabic so I haven't had to go through what people find difficult in English. I do remember having trouble with knowing when to put 'b' or 'd' in a word when writing it. Something about the mirror image of the letters confused me as a kid. I would write something like 'sudway' instead of 'subway', but I think that's a problem most kids have. Spelling is definitely a big problem for learners of English as well as native English speakers. The fact the bomb, tomb, comb all end in 'omb' but don't rhyme is just one example of many that attests to how convoluted English spelling is.
A specific problem to native Arabic speakers that I've written about before is differentiating between 'p' and 'b'. Since Arabic has no 'p' sound Arab speakers will often say 'p' as 'b' like banda bear or bolice.
The difference between 'f' and 'v' also comes up because, again, there is no 'v' in Arabic. So you will hear many Arabs say 'fery' instead of 'very'. This isn't as widespread at the 'p' vs. 'b' thing though.
The fact that English has many vowel sounds while Arabic only has a few is another problem. The words 'pit', 'pet', 'put', 'pot', and 'pat' might be the hardest in the entire language for Arabic speakers to pronounce and recognize. Words that are only differentiated by their vowel sound are tough. I know a guy who couldn't hear the difference between 'bomb', 'pump', and 'bump'. The 'o' and 'u' sound were hard for him as well as the 'p' and 'b'. The difference between 'six' (6) and 'sex' also causes problems. The 'e' sound in 'sex' just isn't found in Arabic. Many will say 'sixy' instead of 'sexy'.
These mistakes don't cause too much difficulty in being understood though. As long as the word that is said incorrectly is in a sentence to give it context it's fine. However if someone just asks you what X means and they're saying it wrong (like asking what pit means when they actually are trying to ask what pet means), then you can run into problems.
What are some more difficulties people and especially Arabic speakers face in learning English?