Even though I can mute the guy calling me every name in the book, he's gonna get punished before the guy who intentionally fed in my game before going afk. Why? And don't say "The system can scan chat logs so it's faster" because it can also detect an afk. So why will he get off with nothing while the guy who called me a name will be punished ASAP?
Detecting an AFK is infinitely easier than detecting a troll or an intentional feeder. You can do it yourself if you've got any programming knowledge, use the Riot API and look for players that stay in the exact same spot minute after minute. Done, easy.
Next easiest is intentional feeding. Someone building boots of mobility and 5 zeals is easy to detect, and Riot detects them (they made a post about it a year or so ago). Someone who also dies over and over, minute after minute, also raises some red flags. But you have to not be too greedy and peg people who are unskilled or playing in a different but valid way (proxy Singed, for example). I genuinely had a 0/13/0 teammate who wasn't intentionally feeding, they were that bad.
Trolling is very hard to detect. What's the difference between high elo players duo Jungling during a lane swap and a troll who's following the Jungler and trying to steal camps? To the computer, absolutely nothing, they're the exact same play pattern. You've got to get a computer to recognise that specific pattern of trolling and create a very specific way to check for it that doesn't hit valid play styles.
As for language, that's significantly easier than trolling to detect because other companies already developed the software. You just plug in their language detection to your chat system and away you go. Depending on the system used, it's possibly easier than Intentional Feeding to detect.
Ultimately, language was prioritized because of Leagues reputation. It wasn't known as the game with the most intentional feeders, nor as the game with the most trolls, nor as the game with the most AFKs. It was known as the game with the most toxic community. That's something that doesn't do well for getting new players to join, so of course the priority would be fixing that reputation. They're turning it around, but if the chat logs that show up on the boards are anything to go by there's still a ways to go.
