I think we may safely blacklist ALL bookmarks - they aren't appearing on the Kindle anyway
As for media player... I think you're wrong.
My media_player_bar_string.js is in UTF-8, and constructor gets its arguments in UTF-8.
This "MessageFormat" thing isn't handled by Webkit I suppose, seems like it's handled by that icu4.jar file I pointed at above.
However I'll try your new tool this night and we'll see if it helps with media player or not.