> People may have presented the concept before the US Constitution but it certainly didn't apply to many people legally (if any?) before then

You may want to check out topics such as Freedom of religion, the Peace of Westphalia, or Ancient Greece.

I don't know what the eastern equivalents would be, but I suspect at various points in history that individual freedoms were won in China too. Maybe Confucius is a good starting point.

And how many people had freedom of speech in 1750.

Ha and try offending the emperor of China to his face in that era (or now) and let me how long you keep your head for.

Freedom of speech is not permanent. It has to continually be demanded, or it disappears. There will always be people trying to tell you what to do or say. If you don't decide for yourself, someone else will decide for you.

They never mentioned "legally" either, so why are you bringing that up?