Unfortunately ICU is required for normalization, except in win32, where I wrote it in win32 natively (as normalization is native to the OS and boost doesn't link ICU statically in Win32). Boost also fails to link statically on Linux/macOS, but we work around that with a hack. They explicitly don't like static linkage for ICU, which is stupid.
https://svn.boost.org/trac10/ticket/9685