To allow utf-8 aliases in Japanese (and multibyte characters encoding in general), besides commenting the line as stated in the first post of this thread, you also need to alter access to the DB to have ModX to store "real" utf-8 characters in the database:
Basically, what I did is below each line like:
@mysql_query("SET CHARACTER SET {$database_connection_charset}");
I added the following lines:
// set encoding information
@mysql_query("SET NAMES 'utf8'") or die("Could not run set names.\n");
@mysql_query("SET character_set_server = utf8") or die("Could not set character set.\n");
Now, aliases are automatically urlencoded and the pages are retrieved normally.
It’s dirty, but it runs!