"In Esperanto you can create a new word."
Translation:En Esperanto vi povas krei novan vorton.
Esperanto isn't 100% logical, it is not Lojban. So "en" can refer not only to spatial concepts (en la domo), but also to temporal ones (en la jaro 2002), and to abstract concepts (en tiu situacio, en Esperanto, en amo).
"Per" works but means something different, more like "by means of".
"En Esperanto oni povas krei novan vorton." According to my knowledge "oni" means "one" in English, not "you". So the translation would be "In Esperanto one can create a new word". In the Dutch language I would translate this sentence to "In Esperanto kan men een nieuw woord maken/creëren". I wouldn't use "je" (="you").
Mizinamo is correct, oni can be translates as both "one" or "you". Both are fine. With your very same argument you could also argue that "one" is a wrong translation of oni, because "one" is unu in Esperanto.
In other words: Yes, "you" is one of the possible answers for oni.