Pretty cool little trick I discovered, for anyone like me who plays lots of league, and interested in learning another language. In your config folder, you simply edit the LeagueClientSettings.yaml file, and edit the globals: locale to something like "es_MX" to switch the language to Spanish instead of English. You have to do this while league is closed, and then save the file and open league, to see the change.
Obviously your in-game chat will still be in English, so it doesn't affect your ability to play the game or chat with your allies. But all the buttons, item descriptions, patch notes, youtube video links, even the announcer in both the client and in the game will ALL be Spanish.
If you've been playing the game for years, you probably already know every announcer quote and every text in the game. So now it will all be in Spanish, and your brain will be working to try to translate it based on your memory from having played the game so much.
And that's pretty much it, you'll be immersed in Spanish, which is one of the best ways to learn. In just a few months you'll probably know a hundred Spanish words. And within a year you'll be reading the patch notes and understanding or guessing 80% of the words without needing to look them up.
But just so you know, switching to "es_MX" also means that you are switching not just to Spanish, but to MX which is Mexico. So all the news on the first page of the client, will be news related to popular teams in Mexico. So if you do this, be prepared to get a blast of Mexican culture as well. :-)