There is an academic research body called English Profile. The founding members of this group are Cambridge and Birmingham Universities and the British Council. They have divided up English vocabulary for learners into levels according to the Common European Framework level system, where the following bands indicate these levels of proficiency:
- A1 (Beginnner/Elementary)
- A2 Pre-intermedate
- B1 Intermediate
- B2 Upper Intermediate
- C1 Advanced
- C2 Proficiency
The research they undertook was to see what words are actively being used by learners at each of the different levels. They used a large corpus of learner English to do this, primarily taken from the Cambridge Learner Corpus, but also from the Cambridge English Corpus.
These vocabulary bands could easily be used as a starting basis for determining the level of difficulty of acquisition. The Original Poster would then probably want to go through the different bands with an eye to things that would make specific items more or less difficult for an Arabic speaker.
Things to consider in this regard are: false friends, pronunciation issues (words with /p/, /v/, /f/, /g/, for example are going to be slightly more difficult for learners to successfully acquire. So are words with clusters of three or four consonants, as none of these English clusters occur in the onsets or codas of Arabic syllables), the grammar associated with specific items, and how cultural differences may affect the interpretation or usage of particular items. The Original Poster will probably be best placed to predict what other problems there may be.
For more information on Englishprofile, click here
To try out the English Vocabulary Profile searcher click here. You do need to register your email address and insitution details, but it's completely free to use.