Other things being equal, the closest language to your own is the easiest. Since your native language is Arabic, the closest foreign language would be Hebrew, which you could pick up relatively quickly. Amharic, another semitic language, has a fairly large number of speakers. Between German and Spanish, it seems that other things being equal, German tends to be significantly harder than Spanish. Knowledge of English helps with German (and a little bit with Spanish as well), and knowledge of French helps very much with Spanish. Really though, the easiest language is the one that you love to learn.

It’s different for everyone. The easiest language to learn is the one that is very familiar to your native language or close to the language(s) you already know.

I agree with Phil. Objectively Hebrew would be the easiest language because it’s related to Arabic. Between Spanish and German, Spanish will be easier. It has a simpler grammar than German and more loan words from Arabic. But the easiest language will be the one that you feel passionate about because you’ll be motivated and enjoy the learning process. Ask yourself, why you want to learn these languages. Unless you need the languages for your career, let your heart choose.