I'm one of the Welsh learners on
Polygloss - there are lots of us, many migrated from DuoLingo I think. It's dead easy to use, and 'addictive' but in a good way - there's no pressure, you just feel stimulated to keep using it, writing something in your target language to keep the conversations flowing (you earn a 'reward' if someone else appreciates your creativity). And it also feels good to pay back by helping those less fluent, if they make an error.