I just had a chat with the Support team asking them about changing languages in League of Legends. Like a lot of player I am using the Japanese client for my EUW and EUNE games, I am NOT altering or changing the files in anyway, analysis have been made and even full repair does not detect anything suspicious. I simply type in the "system.yaml" file what I want, hence making the game patch itself to Japanese. Sometimes when there is a special event (like the Poro Mart last Christmas for JP), I do have it on my client aswell and cannot interact with it obviously, I'm here to play not to cheat. Just to say that changing languages IS possible, I can already do it myself withing 20 seconds, the downside being my full client in Japanese (I learnt the basics so I'm fine using it) but seriously... Wouldn't be more simple to give players the ability to choose the voice language directly from the client (like a LOT of games already do) ? We wouldn't risk ambiguous discussions with the support team. You could even made voicepacks that would need to be paid in RP, I would sure spend them in Korean and Japanese voices. We should be free of enjoying voice actors we love, not everyone has a connection good enough to afford a decent ping in the Japanese servor (I sure don't).
This question is popular, it has been asked for years now but I am bringing it back because we know it's possible. I shouldn't be forced to type in my "sytem.yaml" file after every patch for something that simple, I shouldn't have to play fully in Japanese to just hear the voices I love. I'm pretty positive it would take your teams few time to make it happen, and if you have higher priorities (which I'm sure is the defense you'll use)j just take those 5 mins, make payable voicepacks if you want to ! Imagine, launching your client and instead of having only one window in the language section you'd have 2! One titled "system language" and one titled "voice language".
Once again, it works, these are RIot's official files, present in your folders by simply clicking on the region you want: if you click on Japan, your client restarts and loads JP client and JP voices, just make it easier, allow people to choose their language directly from there, but only the voices :D
PS: SINCE YOUR LATEST PATCH IT DOES NOT WORK ANYMORE, as the other copies of the "system.yaml" files are missing ! BUT THAT DID NOT STOP ME, there is a nother file called "LeagueClientSettings.yaml" that you can change