Add Korean (ko) as an interface language

[zereight]

Hi,

I want to add Korean (ko) as interface language. Right now app has English and 9 other languages, but no Korean. Korean users have to read English menu and setting, and some words are hard to understand for them.

I read docs/i18n.md and the "Add a language" steps. I can do the registration part first. After that I will translate the catalog. As CONTRIBUTING says, it can be partial at the start.

I have two questions before I start:

1. Speech level. The terms part of docs/i18n.md says what each language uses (Japanese uses です・ます), but nothing about Korean. My idea is polite style (해요체) for sentences, and short plain nouns for buttons and tabs. Is it okay? Or do you prefer formal style (합니다체)?
2. Terms. The terms table has no Korean column. I would add one for the same words (agent, chat, conversation, channel, server, host, skill, routine, workspace, provider, Settings). Should I add it in the same PR, or in a separate one?

If the direction is good, I will open a PR. It will be big, like the Russian one (#1548), because many catalog files change.

Thanks for reading.