Sounds like a job for MIT or BSD 3-Clause.
(Or Apache 2.0 if you also want people to “cause any modified files to carry prominent notices stating that You changed the files” - i.e. leave a comment saying
// Edited by so-and-so.)
That’s also doable.
Creative Commons licences are more suited for sprites.
Wikipedia explains the general idea quite well here.
Generally country of origin makes little difference in regards to licences.
Creative Commons licences are specifically written to be as universal as possible.
(Part of the reason CC0 even exists is because some countries make it really hard to put things into the public domain, or don’t even have a concept of ‘public domain’.)
Most software licences aren’t quite as meticulous,
but should probably work the same everywhere.
I think most of the warnings were probably related to
Entity::getSprite so there may not be as much of an issue as I was first expecting.
The only real issue would be how to handle the entity type being