Not seeing the Polish letters ą, ę, or ł anywhere on the keyboard. Poland is in Europe, too.
(â and î are even needed in French, what am I missing here?)
I'm sure there must be many other letters missing. Not to mention Bulgaria and Greece.
No qualms with the layout, it's probably impossible to cram all European letters and common programming symbols on only ~four layers -- it's just the name that's somewhat provocative.
Interesting reference: https://jakubmarian.com/special-characters-diacritics-used-i...
à á â ã ā ă ȧ ä ả å ǎ ȁ ȃ ą ạ ḁ ẚ ầ ấ ẫ ẩ ằ ắ ẵ ẳ ǡ ǟ ǻ ậ ặ
You'd need to hold down combinations of 5 different modifier keys, and shift can't be one of them because that's used to capitalize all this. Nobody's going to do that.