So, I'm not sure if this is a common problem, or if this solution is common knowledge, but here goes.
I'm a regular user of LegendsViewer and LegendsBrowser, and for the longest time I've been almost completely unable to get them to work properly with RotMK. But today, I finally found out why (and really, had I paid more attention to the error messages I would have solved this sooner).
It seems that a lot of the unicode characters that the Shyguy language uses are considered invalid. Even when I view the language file in Notepad++, I see a lot of black unicodes, rather than actual characters. This includes things like the double exclamation marks, and the musical notes, as well as a few others. These characters caused LegendsViewer to think the XML file was corrupted, and the LegendsBrowser would just keep saying "invalid unicode character 0x1". By replacing all of those strange unicode characters in the language file, I've managed to get it to work. This DOES remove the neat little characters, like the hearts, musical notes, and such from the game, but it also lets me use LegendsViewer, which I practically
need to play DF.
If there's some other solution I could have done to make LegendsViewer work and STILL have the characters, feel free to let me know. But for now, thought I'd put this here in case anyone else who has the problem I had comes across it.