My dad had to learn both Old and Middle English as part of his English doctorate, but he didn't know German. I guess he could have learned pretty easily. He was great with languages. He was actually offered a job by MI-5 as a Russian translator in the 1950s, but as he was a socialist, he told them to fuck off.
He learned Russian because he loved Russian classical music. Really. And then he studied the language the rest of his life. I remember him doing self-written grammar conjugation flash cards when he was in his 70s.
I'm learning German but all I got out of that was "endlich ich mag(? Not sure)" and something something "meine Sprache". I can't find a good translator to check the whole sentence
Esperanton is the accusative form of Esperanto. So literally "Do you speak Esperanto?"
Esperante is an adverbized form of Esperanto. So "Ĉu vi parolas esperante?" Is like "Do you speak esperanto-ly?" Hard to translate literally.