I have a bit more info about the broken fonts - it seems to be a combination of the font name possibly containing a space and the locale of the Kobo. For example: "Charis SIL" is broken irrespective of locale, I think because of the space in the name.
As an experiment I created a copy of the Charis SIL font and called it Charisas (no space in the name). Now the "Charis SIL" font only defines a language of "English - United States". The locale of the Kobo is set in the .kobo/Kobo/Kobo eReader.conf
file (see http://www.mobileread.com/forums/sho...d.php?t=206200
). This defaults to a US locale (CurrentLocale=en_US) which worked with my new Charisas font (without the space in the name). However, I had previously changed the locale of my Kobo to en_GB (to get dates in DD/MM/YYYY format) so I also had to add a Language "English - United Kingdom" to my Charisas font, and hey presto, it now works: bold
are now working on 2.4.0.
Something broke between 2.1.5 and 2.4.0 in how the Kobo finds fonts, to do with the font naming and the device's locale. This should be fixed by Kobo, but at least we now have a workaround.