Anna, here is a link for you leading you to some free and excellent resources for an introductory study of Arabic:

http://www.fsi-language-courses.org/Content.php?page=Arabic

I suggest that you start with the resources on Written Arabic. This would help you most at this stage.

You can download the materials and do some offline studies if you want and if you have time.

Let me tell you something from my own experience: English is one of the those second languages that I can master more or less accurately. I have even published some of my books in this and other languages (in addition to English, there are some of my publications in Chinese and German, and others). I have written these texts in the languages concerned myself, they were NOT translated. These texts were, of course, edited and corrected by native speakers. As a former university professor, I have given many of my lectures and courses in any of these second languages.

With that background in mind, I would say that you can teach English as a Second Language to non-native speakers of English without the need to know something about the native language(s) of the learner(s). But it would help if you knew some essential basic things about the native language of the learner as this might have a positive impact on your teaching strategies and methodologies.

To make a long story short, let me encourage you again to learn the Arabic language. It is a great language of a great culture, and in the end you will also learn a lot about yourself and your own language and culture when being able to compare.

Again, good luck!