The OSUser and Atlassian-User authenticators used by Confluence convert a password into bytes before hashing it. This conversion doesn't specify which encoding should be used, so the system's default encoding is used.

If the system administrator changes the locale settings on the server or changes the 'file.encoding' system property value, users with characters with a different encoded value in the old encoding will not longer be able to authenticate. For example, if your password was 'café' and you changed from Latin1 to UTF-8, you would no longer be able to authenticate.