/u/HOUNDfre as for your edit,
edit: can you actually explain why is it such a resource-draining job when third-party apps can already do this? I understand that no way im getting an honest answer here but whatever, asking doesn't hurt
There's two sides to this. Why can third-party apps do this and why does it take a lot of time for Riot to do this correctly. When a player modifies their own client, either by themselves or via a third-party app, then the changes are localized to them. If the client breaks it only affects them and they can easily just re-install the client or remove the app. If we do this and it's done poorly, it'll affect millions of players.
Now we're wandering into territory that I'm not the subject matter expert (sme) on so some of what I say might be inaccurate, but it'll hopefully provide better context. If it wasn't clear, my subject matter expertise is in third-party apps.
- Every region tailors content to it's own player base, this is because some content makes more sense in some regions than it does others. This is why we name skins differently in some regions vs others allowing for things like localized puns and such. As such not every region sees the same content and therefore isn't localized. If we were to just enable every language, then there would be content that missing or just not localized at all. Then we'd have players asking why we shipped a half-baked experience. If we wanted to do this correctly, we'd have to localize each regions content into ~29 languages and create a new content management system to ensure all this localized content was delivered at the same time and properly managed by the client.
- Okay great, lets say we decide we bite the bullet and take the time to do all of #1, now we get into the technical hurdles. A lot of the content that isn't on-demand like the News Page, is shipped with the client itself. Think the tooltips, the profile page, etc. Everything that doesn't change between patches is usually just packaged and shipped altogether. Well if you're supporting 29 different languages now you gotta ship a package that is much larger than if you only ship 1 language or 5 languages. Now I live in the US, so I pay a flat fee and get unlimited home internet. No problem I don't care if it's a 500mb patch or 2gb patch. I've even got 100Mb down so maybe it takes under 2 minutes to patch. Well if we ship 29 different languages with every client, we're kind of giving the middle finger to any player in regions around the world where unlimited internet isn't a thing. Some places you're charged by the gigabyte or you have a monthly cap. In fact in some of the regions, I believe we make USB sticks and ship it straight to the PC Bangs. In some regions it can take 30m to an 1h to patch if they did it over the Internet (instead of local installs). What if we added those 29 languages there? So now we're talking about making the content optional, we have to change the way we ship content in the client. There's a lot of ramifications here.
Again, there are parts of this that may be inaccurate, but hopefully I've illustrated the point of how it's not as simple as let's enable language drop down in every region. I truly believe the experience would be disjointed and arguably worse.
edit: I'm thinking about this a bit more, and I believe #2 is actually less of an issue than I originally mentioned. I believe the client already optionally downloads some content. Not sure what extent, but that's why the client usually patches when you switch regions or languages. I believe that's the localized assets being changed. Hence my hesitation to go this deep in the first place and leave it at, the simplest reason is there's higher priority work. I should stick to explaining third-party apps :(