Changing the language picker should take you to index.html if translated, but doesn't

[cannikin]

Right now, even if index.html is translated, changing language will take you to the latest version of the spec. It should take you to the translated index.html:

Steps to Reproduce

1. Choose 简体中文 as your language
2. Page redirects to https://deploy-preview-34--toml-io.netlify.app/cn/v1.0.0

Expected Behavior

Should redirect to https://deploy-preview-34--toml-io.netlify.app/cn/

[LongTengDao]

Supplement:

1. When click Version -> v1.0.0 from toml.io/cn/, the page should go to toml.io/cn/v1.0.0, but currently it is always toml.io/en/v1.0.0.
2. In page toml.io/cn/, the button Version need to have a way to show i18n content in translated index.html.
3. Maybe English should be the first option in languages select menu.