convmv is meant to convert the filenames in a directory tree or a
whole file system into a different encoding, with support for
symlinks.

This is useful for converting from old 8-bit locales to UTF-8. It is
also possible to convert directories to UTF-8 that are already partly
UTF-8 encoded.

convmv can convert names to both the NFC and NFD normalization forms.
NFC is commonly used on Linux and (most?) other Unix-like OSes,
though does not enforce it. Darwin, the base of Macintosh OS X,
enforces normalization form D (NFD).