Chinese or Arabic???

Just my two cents, as an American speaker of two non-Western languages - there are lots of Chinese out there, and they're all learning English. If you plan on doing business there, my sense is that their English will almost always be way better than your Chinese. Unless you plan on moving to China and living there for a long period of time, during which you could conceivably gain some level of fluency, I say go for Arabic.

The pool of Western Arabic speakers is probably way smaller even than Chinese speakers. It's still a *complain* to learn (trust me, I know), but probably a bit easier than Chinese. Also, consider that you'd have to decide between learning Mandarin and Cantonese - which may have a lot of similarities, but are essentially different languages for someone who's not fluent already. MSA (modern standard Arabic) is more or less the same everywhere. Spoken Arabic is often different, but standardizing quickly, thanks to al-Jazeera and the Lebanese. And let's face it, it sounds cooler.

But again, unless you plan on moving somewhere where one of these languages is spoken, it's unlikely you'll ever acquire any considerable level of fluency.