Light C Unicode Library [closed]
UTF-8 is specially designed so that many byte-oriented string functions continue to work or only need minor modifications.
C's strstr function, for instance, will work perfectly as long as both its inputs are valid, null-terminated UTF-8 strings. strcpy works fine as long as its input string starts at a character boundary (for instance the return value of strstr).
So you may not even need a separate library!