As a tourist it shouldn't be an issue, but if you want to work there (not that there is really much to do outside big cities) you will have issues if you don't

As a tourist it shouldn't be an issue, but if you want to work there (not that there is really much to do outside big cities) you will have issues if you don't speak Lithuanian or Russian. But that's the same as if a non-French speaker tried to find work in somewhere like Valence.