Another brazilian mastodon instance: https://bolha.us/about The administrator also hosts Peertube, BookWyrm, Pixelfed, Lemmy (instance i'm using) and others.

For learning japanese I would not recommend Duolingo, people often recommend using The Moe Way, Tae Kim and Organic Japanese with Cure Dolly. I'm just a beginner, but I tried learning with duo and it was not good. Learning using The Moe Way was way more faster and logical