feat!: Implement localization support into Yari (and localize BCD tables)

[queengooborg]

This PR introduces localization of the Yari platform itself, so that translators can localize the platform's common elements as well as the content. It utilizes react-i18next to do as such, a top rated localization package for all of NodeJS. (This is a pretty big change as it introduces a brand new API for handling strings.) As a proof-of-concept, I have made the compatibility tables localizable.

Design

For the strings, the i18next format is used, which handles variable interpolation, formatting, pluralization, arrays, and more. While i18next uses the handlebars format (that is, {{ }}), TypeScript wasn't happy with this, so I switched the delimiters to two square brackets ([[ ]]).

The setup also takes advantage of the multi-file structure provided by i18next, which means that translations may be separated into multiple folders for each language, and multiple files for each group of strings (called "contexts"). In other words, strings specific to the BCD tables may be stored in bcd.json, while navigation bar strings may be stored in navigation.json. With the multi-file structure in mind, I've set it up so that localization may live in mdn-translated-content rather than here in Yari. All translations will live in one repository, with files for Yari's platform localization stored in files/<locale>/_yari/<namespace>.json.

Translation Steps

To translate the strings for the Yari platform, translators may perform the following:

• Copy a file from mdn/yari/client/i18n/ in this repository and paste it in mdn/translated-content/files/<locale>/_yari/
• Translate each string within the JSON file
  • Any strings missing from the copied file will default to English
• Repeat for each file in the i18n folder

[SphinxKnight]

poking @mdn/localization-team-leads regarding the topic here :)

[github-actions]

This pull request has merge conflicts that must be resolved before we can merge this.

[queengooborg]

(I've got no clue why the Developing with Yari test isn't working...I'm not having any problems with it on my end.)

[queengooborg]

I now see that the same test script is failing in other PRs as well:

https://github.com/mdn/yari/runs/6502514714?check_suite_focus=true
https://github.com/mdn/yari/runs/6464968135?check_suite_focus=true

So I'm not worried about that test run any longer.

[github-actions]

This pull request has merge conflicts that must be resolved before we can merge this.

[schalkneethling]

Hey @queengooborg! Thank you so much for this pull request. This is amazing work. We are discussing this internally and will reach out to you soon.

[Jalkhov]

Just for reference mdn/translated-content#6943

[github-actions]

This pull request has merge conflicts that must be resolved before it can be merged.

[caugner]

Converted to draft pending our decision on how to move forward.

[github-actions]

This pull request has merge conflicts that must be resolved before it can be merged.

[github-actions]

This pull request has merge conflicts that must be resolved before it can be merged.