I figure—a mod titled "World Flags" with only 44 flags in it? That's not really the world. I've taken it upon myself to create a submod that lets World Flags live up to its name, aptly titled:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2047628891
Current functionality: it adds 250 new flags and overhauls the existing UI to add tabs for each continent, that way the list doesn't get too bloated.

As of writing, this project is far from complete. But I've made a few tools—an effect plugin for Paint.NET that makes spriting drastically easier and batch files that automatically generate the .object, .frames, and .recipe files—to make adding flags incredibly streamlined.

The project GitLab is here: https://gitlab.com/MoofEMP/starbound-more-world-flags

If you'd like to contribute, feel free to fork it and create a merge request with a few more refs or a few more flags (or just one), and I'll credit you. If you don't know how to use git, and you just want to make pixel art for it, you can even just send me the refs and I'll include them and credit you. I don't expect this project to really become huge, so I'm the only project member and I'll personally audit any changes.