So I had to settle with WinCompose to do proper non english languages.
https://github.com/samhocevar/wincompose
Did anybody get this fixed in Windows? If so, please send help! Also if you are inside Microsoft and know the correct team to adress this to, please for gods sake, point them to this issue.
Asian languages are harder. But if you're told about IME, then at least if you know what you want to type, how to actually type it isn't a big burden. IME can also help with rarer math symbols like โ (\bigcap) โ (\cong) or โต (\unrhd), or is another way to get something like the compose key system.
I recommend WinCompose: https://github.com/samhocevar/wincompose
On Windows, I use WinCompose[1], which works decently well.
[1] https://github.com/samhocevar/wincompose (Trivia: WinCompose was originally written in AutoHotkey!)
For example:
โ - - - produces an em dash (โ)
โ - - . produces an en dash (โ)
โ ' e produces รฉ
โ | c produces the cent symbol (ยข)
Usually, you can just guess the combination and be right 3/4 times. Otherwise, it's fairly easy to look it up, or create it if it doesn't exist yet.
Some distros of Linux have this built-in, but I use WinCompose[1] on Windows.