[REQUEST] i18n / Translations for ember-website

I would like to see the ember-website support translations.
Not only just displaying them, but providing an easy way for experts in other languages to contribute and improve their language as well.

This is _vitally_ important for Ember's growth as a _English_, while the most common language in the U.S., is only 4th in the world, behind Chinese, Hindi, and Spanish.
Though, depending on who you ask, these change order a bit.
Source: https://en.wikipedia.org/wiki/List_of_languages_by_total_number_of_speakers
_Sorted by the number of first-language speakers_

The important part is that _most_ of the world does not speak English as their first language, and to welcome the rest of the world, make them feel more comfortable, at home, etc, we should offer translation options for the main web sites (ember-website and ember-guides).

I don't believe an RFC is needed (though I may be persuaded if enough details come up) for this as each web-site-app needs its own separate implementation for how it handles translations -- resulting in either one RFC for public website, or infinite bike shedding over details (which we don't want 🙃 ) Incremental progress is way more valuable than getting something right in this case. The fundamentals should be straight-forward -- like I think we can generate pages in each language for SEO purposes -- _how_ can be discussed on PRs.

For example:

- ember-website: probably whole translation files (traditional style), since this site is, content-wise, the simplest
- ember-guides, maybe similar to how translations are already handled on the ember classic to octane cheat sheet: https://ember-learn.github.io/ember-octane-vs-classic-cheat-sheet/ There is an insane amount of content on the guides, and breaking it up would be a huge benefit. There is, of course, a huge technical challenge with the guides around versioning, but that can be solved later.
- the API docs are probably the hardest to deal with as they are docs-generated-from-code -- I know the learning team has some thoughts how to greatly improve the API docs so that older versions' docs can be updated without releasing ember-source and friends again, but that's also a big effort.

I think it'd be great if we standardized on some sort of language-picker the top-right of every site.

I know there are some opinions that "we shouldn't provide translations until there is interest", because maintaining docs is _really hard_, and doubly so for additional languages.

I must ask that everyone consider that folks could be alienated if they see that, no only are there currently no translation efforts underway, but there is no easy way to submit a translation to any of the sites. And the technical challenge of setting up translations in the first place is far greater than someone can bare if they are new to our ecosystem.