The answer is twofold. One, the video needs to be publically accessible. If you could just send it to a single mod, then you would only need to convince one mod to submit any time you wanted. Mods are chosen for trustworthiness, of course, but there's been scandals in the past where big video game communities had a single mod that turned out to be complicit in faking scores, if not faking scores themselves (shoutouts to Twin Galaxies).
Two, speedrun.com can't just host the video themselves because videos are relatively large files, and speedrun.com has thousands if not millions of runs by now, and they do not have the money to store that many files, let alone serve them to all comers over the internet.
For one thing, the manip does not work on Virtual Console, only on game boy advance, Game Boy Player, Super Game Boy 2, and the gambatte emulator.
Can you tell us which videos you were watching so we can better understand what you're asking about?
Most speedrunners use English but a few use Japanese, it's just a matter of which version a runner has.
It's already there in category extensions; runs used to be done in it before it was discovered you could use BLJ to skip the 50-star door.
yeah you press A once to put the one letter in the name, then you press Start -- this also works on naming rival, squirtle, and nidoran.
if you have any more questions hmu on discord or ask in the gen 1-3 speedrunning discord, although I don't know all the menuing tricks, which is the main reason I'm so low on the leaderboards
GBC, GB Player, or GBC emulator (gambatte) are fastest because those are the only ones on which the known RNG manipulations work, as they are BIOS-dependent. All three should be equivalent in speed.