Updating icu4c on macOS - enabling-languages/intro-python-i18n GitHub Wiki
If you update icu4c, by itself, you will break pyicu. It is necessary to update icu4c then uninstall and reinstall pyicu ignoring the cache:
brew update
brew install icu4c
pip uninstall pyicu
pip install -U --no-cache-dir pyicu
or
brew update
brew install icu4c
pip install -U --no-cache-dir --force-reinstall pyicu