There is no question that it is best to learn in the original language of the writer.
Regarding “clean” languages, there really isn’t any such thing anywhere in the world except for newly invented languages such as Esparanto. There are Aramaic words in Chumash and entire sections of Tanakh are in Aramaic. The gemara is full of Greek words and I even found a Latin word in the Mishnah. Rashi translated words into French for his audience — so many that medieval scholars use Rashi’s translations as a major resource for understanding the Christian and secular writings of that time. (Derech HaMelech, I’m not sure what you mean by “don’t talk about”.)