French title released: Les derniers Jedi. Yep, plural, so several Jedi are expected.
I know of at least one language where the title was translated in singular. So this does not seem to be very reliable.
A mistake can be made in one way, but not the other way.
In french, you just can’t translate “The Last Jedi” in plural by mistake.
What do you mean you cannot translate “The Last Jedi” in plural by mistake? “The Last Jedi” in English can be both plural or singular, therefore you do not know which one is it when you are translating.