Before going deeper with RR and Unicode, there are a few things to mention:

1-If you only use English (or any language without accents/or different characters), there's nothing relevant to you on this thread -- no need to read any further.
2-If you only use ONE language (or just one language BESIDES English), you should set the Default Language Non-Unicode applications to the language USED. This can be done by going into Control Panel->Regional Settings->Advanced and selecting the language you use from the Drop Down list. IF you do this, there's no read to read any further.

If you're reading from this point below, we assume you want to use MULTIPLE languages, meaning: TWO or more Languages that are NOT English (regardless of using English at the same time or not).

First, you should decide what language you use THE MOST and configure it as your Default Language Non-Unicode applications (Following instructions on "2" above).

On that language selected above (and English), there are no limitations of what you can do.

With any OTHER language used (asides from English and the language selected above):

There's a new "term" being used/defined here: NWU (Non-Western Unicode) -- Those are any special characters that are not within the standard English/Westen Character set which is basically A-Z, 0-9, space and basic symbols like parenthesis and such. Anything that is not in the western alphabet (i.e. Chinese, Japanese, Russian, etc) is considered NWU here (except for anything in the language selected above). While RR can handle NWU for display and playback, certain features will not work if you try to use NWU with them, listed:

-Run RR from a NWU path
-Use the Winamp Library when running Winamp from a NWU path
-Save/Load Custom List to/from a NWU Path/Filename
-Have a NWU Skin folder name (very unlikely)
-Have any skin files with a NWU names like .skin files, image files, etc (very unlikely)
-Save/Load a Playlist to/from a NWU Path/Filename
-Save/Load a Mixer Preset into/from a NWU Path/Filename
-Put TV Presets on a NWU path
-Use writetofile/addtofile/addtolist into a NWU Path/Filename
-Browse into M3U(8) file with NWU name or in a NWU path (improvement planned)
-Use TEXTART with NWU Path/Filename (improvement planned)

Again Notice: The features above should work 100% in English and the language you select in control panel (Following instructions on "2" above). The limitation is only on using characters from OTHER languages with those features AT THE SAME TIME.

ID3v1 Note: ID3 V1 tags CAN have special characters in other languages (than English) AS LONG AS you select the desired language in control panel (Following instructions on "2" above).