If I am planning to travel..?

in Shengen, what languages would I need to know. I only plan to go to Sweden, Finland, Italy, France, and maybe Germany. Would I need to know Swedish/Italian/French AND German? I know English is spoken in Sweden but i want to learn Swedish to understand my enviroment. From what I understand, finnish is comprehensible to Swedish so if I knew Swedish would I need to learn Finnish? Thanks