Indeed, special characters are not correctly encoded in UTF-8 during the runClient (after clean build). This is all the more visible by activating the English upside down language and that the name of an item only looks like a bug. I am creating a French translation of the mod (#1419) and this language has a wide variety of letters with accents (bugged too in game after compiling).
I analysed the code and I think the bug comes from the herblore.json file in the src/main/resources/assets/font folder but i don't know how to fix it.