As far as I know, utf-8 works. Although being from the USA, I've never had occasion to even try it.You need to post some details about what you tried, the version of fvwm you are using, etc.
It's my fault, I was answering via Roundcube which doesn't work with the mailing lists very well.
The problem was most likely because of a mistake in XLFD string which led to using a fallback font. That, or a font without needed glyphs.
Solved by using "xft:Font Name:size=somesize" instead.
