From what I learned when helping a friend research this topic, the rules can be a bit different depending on the path to citizenship, but in many cases when people apply through ancestry the language requirement isn’t the main issue. My friend was also worried about that at first because nobody in his family spoke Lithuanian anymore, yet his grandparents were originally from there. While looking into the Lithuanian citizenship restoration process, we tried to find reliable explanations about the requirements, and one helpful page discussing lithuanian citizenship by descent was here. It explained that ancestry and documentation are usually the key factors rather than language ability. In fact, my friend focused mostly on gathering birth records and historical documents from archives, and the language question ended up being much less important than he initially thought.