Well, if I were to post it to a community on e.g. feddit.org, I would write it as:
Welche Fremdsprachen sprecht ihr so?
“Fremdsprachen” just means “foreign languages”, since I know that responding folks speak German.
Then “sprecht ihr” rather than “sprechen Sie”, because addressing a group of people with direct pronoun is unusual in German.
As someone else already said, using “Sie” is also far too formal for this context. People refer to each other as “Du” on most of the internet.
But “Welche Sprachen sprichst Du?” still gives me vibes of a marketing firm hoping to drive engagement by referring to people directly.
And then the “so”, I have no idea what that is linguistically, but it basically makes the question more casual. It invites for people to tell a story or to have a chat.