Speaking of Portuguese, I've always found the usage of "ç" to be interesting. I've never studied the language but just from looking at words it's clearly the way to represent the soft "c" sound before a "fat" vowel (a/o/u). How did those words ended up with a "ç" instead of an "s"?

This thread finally made me remember to go look it up and it seems like the "ç" used to be a different sound (/dz/). I guess it evolved to the "s" sound we hear today sometime by the 1700s.

I wonder if that means only words older than the 1700s have the cedilha and newer words would just be spelled with an "s"?

Yes, I always figured it was related to the French usage. Not sure who used it first. Hmm, guess that leaves Þ | Θ - thorn or theta for "th", but I'm less enthusiastic.