I made a Sprite Font Tutorial that links to this thread.
https://www.scirra.com/tutorials/629/sprite-fonts-the-how-what-when-where
One thing I noticed, I had fonts made up that use different Character sets, and when I was importing them, since they weren't in the editor anymore, I had to open Construct2's image editor to see what characters to type in the "Character Set."
Could they be added to the text file?
edit: That would make sharing them in the forums easier too