you can use discross, a web based discord client, its not too practical since you need another device to register the server with discross and not every server supports it.

There is no native Discord app for 3DS and I doubt there ever will be. But just like the reply above me you're closest bet is Discross. It works decent but it does have many cons. One for an example is it's not a Discord USER but a BOT. So to use it you need to invite it.

idk what these guys talking ab there wqs a 3ds discord client before