It’s more about the feeling. I would never use chill when something is gezellig. It feels different.
I think cozy is a better English word.
Here's an example which (again, for me) doesn't quite fit: when talking about a party with music and dancing and saying it is 'chill' we'd mean that it was relaxed, enough space to dance, no drunk idiots, fun overall, and so on. We might add to it that it was 'gezellig', not use instead, but then we'd mean there were also lot of friends around and/or new friends being made. While there's a link with being chill, they could just as well be orthogonal. Like 'it was gezellig but too bad it was so crowded' means it wasn't chill at all.
Technically not, but practically it really helps your chances of being correct.
Without knowing both languages you’re more or less guessing.
It’s really hard for something to be gezellig when you are alone, it almost always refers to the people around you, or a location that you’d be happy to meet people. Like, an empty house or cafe is basically never gezellig.
My god I never expected that would be so hard to explain.
Like, you could go by yourself to a little out of the way cottage, hearthfire burning, super cozy! But it’s not gezellig, because there’s no other people involved.
Did you mistake me, or did I somehow come off as excessively self-righteous?