You can define a second-tier surrogate system in UTF-16 on the last 2 planes (plane 0xF and plane 0x10), which are both private use, to access all codepoints up

You can define a second-tier surrogate system in UTF-16 on the last 2 planes (plane 0xF and plane 0x10), which are both private use, to access all codepoints up to 0x7FFFFFFF. Use plane 0xF as leading 2nd-tier surrogates, and plane 0x10 as trailing 2nd-tier surrogates. I've written a package in go that does just that: https://github.com/gavingroovygrover/utf88 https://github.com/gavingroovygrover/utf88