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.)
@SoniEx2 Oh, yeah, I didn't think you were serious. From what I understand, you're suggesting building in machine translation as automatic localization into the OS. That's probably a bad idea just because machine translation isn't very good, rule-based translation is worse, and using either transparently is a very bad idea simply because of the risk.
@impiaaa Nope. It's all manual. You just shove 100 languages in the same webpage using what I call "alternations" - special Unicode constructs that alternate between different... bits of text.
Language recognition is easier than translation, but this has other uses: the simple "internationali(s|z)ation" case is English and so it should display both the "s" and the "z", alternating between "s" and "z".
Another option would be to perhaps include a country code "flag" after each alternation. Anyway let's stick to the simple case, really, just simple alternations that alternate between multiple options.
@SoniEx2 Oh, I see. Eh, it could work. HTML does have language tags already, to assist clients. I'm guessing it's just not worth the effort since it doesn't really work past the simplest case. And, if you're still talking about actually animating it—doesn't that just make it harder to read?
@impiaaa Well, you'd have animated .txt files...
Pure plaintext animated Unicode art...
The main use-case is trivial stuff like s/z, really.