Language /
Polish from Russian [14]
As someone who once attempted same, only in reverse namely Russian from Polish, learning one Slavic language from another, at least for me as a native bilingual German speaker, was tough owing to a preponderance of numerous "false friends"!
While Russian grammar is rather similar to Polish, they are NOT identical in any way, shape or form. This is only from the morphological end. Both the lexical and semic differences are legion.
What's more, Polish is a pronoun-drop language, Russian isn't.
Pronunciation issues are also significant, being that Polish is way easier to pronounce, in my opinion anyway! Russian palatalscan take a long time to get right, plus the "soft" vs. "hard" l-sound can seem impossible to recognize until ultra reinforced by a patient Russian native speaking teacher:-)
If you wish to exchange experiences in depth on this topic, contact me off line, if you wish, at tarsape@gmail.com My name is Mark.