Hi Max and welcome to MR. Your problem with not being able to write in Russian is very common one here in the U.S. among the children of first generation immigrants. You are actually much better off then many as you say you can read as usually they can't write OR read, they can only speak their parent's native language.

We have classes here where I live for Speakers of Native Language to learn the target language. These classes are designed specifically for people like you who can speak the language but maybe can't read/write or maybe not have complete verbal fluency. By any chance do they have any classes like that in Israel??