One aspect of Unicode that is probably not obvious is that with Unicode it is possible to keep using old encodings just fine. You can always get their Unicode equivalents, this is what Unicode was about. Otherwise just keep the data as is, tagged with the encoding. This nicely extends to filesystem "encodings" too.
For example, modern Python internally uses three forms (Latin-1, UTF-16 and 32) depending on the contents of the string. But this can be done for all encodings and also for things like file names that do not follow Unicode. The Unicode standard does not dictate everything must take the same form; it can be used to keep existing forms but make them compatible.