Nice, I think I'm mostly doing this already (especially for the language / countries stuff).
You mention adding extra titles at the end, is there any recommended practice for movie series? For instance just putting "godzilla" as an acceptable title for all "Godzilla vs. random kaiju" movies? Or for a more extreme example, putting "James bond" as an acceptable title for all Bond movies (impossible to remember all their titles hah). Or is that making things too easy and we should stick to letting people figure out which of those movies the shot is really from?
The James Bond case has already been discussed, a long time ago. And no, you can't add "James Bond", nor "James Bond 12" or anything like that. The game is about guessing the movie, not the movie franchise. Same goes for the Godzilla movies, except when they are actually sequels.
Sometimes, the title is already taken but the movie I want to upload is a different one. I always enter the "tt"-part of the IMDb-link instead - after having made sure it's a legit movie.
Oh - and whenever I upload a shot from a movie already there, I add the missing titles (unless I'm seriously ill like right now). Much has changed over the recent decades...