oh heck.
TTF can have SVG in them.
SVG can have javascript.
interactive fonts.
I mean, not /really/, because "Processing of SVG glyph documents MUST be done with script execution, external references and interactivity disabled," but who's to say there isn't a nonconforming implementation out there somewhere.
This part is interesting, though: "The SVG glyph descriptions may be rendered statically or with animation enabled." So *animated* fonts are still on the table.
still though, 
@impiaaa all I want is "internationali(s|z)ation" to work (switch between the "s" and the "z" once per frame).
@SoniEx2 and that would be possible, with a ligature (which is what I was looking up originally…)
@impiaaa I also want it to work for arbitrary text. so "(good morning|bom dia|etc)" would provide free internationalization for all! Language selectors be deprecated!
@impiaaa (I have actually seriously suggested this before. So I'm still seriously suggesting it. I'm sorry if you think it's a bad idea. They should be nestable and some operating systems could attempt to pattern match known languages to automatically show the user.)
@impiaaa (This should only work for text tho, so you can't have "internationalized HTML" that switches the whole DOM once per frame.)