Article 50 of the Constitution of the Soviet Union granted its citizens not only freedom of speech, but many more rights than its American counterpart.

Which tells you something about how meaningless the discussion about whether a country explicitly grants this right or not is. Whether there's a piece of paper saying you have freedom of speech tells you nothing about whether you have de-facto freedom of speech.

True, but having it in your Constitution is an important starting point. Dissidents in USSR weaponized Soviet C. against Soviet administration, just by asking "Where's all the stuff promised here?" And Soviet Union did a lot to prevent its citizens from reading their C. in full (it was notably absent from schools, and public libraries, reviews, and excerpts were offered instead) which suggests these words on paper had some magic power even if absolutely disrespected by the state.

What an interesting example. I'd never read about this before. The article is [1]:

"In accordance with the interests of the people and in order to strengthen and develop the socialist system, citizens of the USSR are guaranteed freedom of speech, of the press, and of assembly, meetings, street processions and demonstrations. Exercise of these political freedoms is ensured by putting public buildings, streets and squares at the disposal of the working people and their organisations, by broad dissemination of information, and by the opportunity to use the press, television, and radio."

[1] - https://en.wikisource.org/wiki/Constitution_of_the_Soviet_Un...