Use the new i18n-loader-webpack-plugin

[anomiex]

Changes proposed in this Pull Request:

• webpack-config: Use @automattic/i18n-loader-webpack-plugin

  Provide the new plugin as part of the standard set of plugins.

• jetpack: Use @automattic/i18n-loader-webpack-plugin

  Configure the new plugin and remove the hack Instant Search was using to
  work around the problem the plugin was created to fix.

Jetpack product discussion

PT: p9dueE-3MG-p2

Does this pull request change what data or activity we track or use?

No

Testing instructions:

• Is CI happy?
• Configure your site for a non-English locale, activate Instant Search, then search. Is the text in Instant Search's popup translated?
  • If you're using the Jetpack Docker env, you might do jetpack docker exec /var/scripts/fakepot.sh /var/www/html/wp-content/plugins/jetpack to generate en_piglatin and en_rtl locales.
    
• Do the above on wpcom too.
  • Currently to test it on a wpcom sandbox, you'll also have to go into wp-content/mu-plugins/jetpack-packages/production/ and composer update automattic/jetpack-assets=1.14.x-dev to get the new version of the assets package.
  • Also add this filter hook somewhere:

    function wpcom_jetpack_i18n_state( $data ) {
        $data['baseUrl'] = 'https://widgets.wp.com/languages/';
        return $data;
    }
    add_filter( 'jetpack_i18n_state', 'wpcom_jetpack_i18n_state' );

    (that'll have to be added to D70962-code before we merge it)

[matticbot]

Caution: This PR has changes that must be merged to WordPress.com
Hello anomiex! These changes need to be synced to WordPress.com - If you 're an a11n, please commandeer and confirm D70962-code works as expected before merging this PR. Once this PR is merged, please commit the changes to WP.com. Thank you!
This revision will be updated with each commit to this PR

[github-actions]

Thank you for your PR!

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[kangzj]

Hi @anomiex wonderful job! So excited we could get this resolved so soon.
This works for me and looks good. We might want to test WPCOM before merging, left an inline comment.

[kangzj]

in WPCOM, the translation path was resolved to mu-plugins if /plugins not specified here.

[anomiex]

It should be ok since the path now isn't being determined by wpcom PHP code, but testing is a good idea.

Looks like we may have to wait until #21932 is merged first so the TC build on D70962-code will succeed. Or merge this into #21932 then test it with a D70957-code that contains the changes from here too, if reviewers would rather.

[anomiex]

So it turns out testing this is kind of a pain, because the Fusion patch doesn't include the changes to the Assets package but those are required for it to work.

Once I manually apply those in my sandbox, it almost works. It tries to fetch the right path, but apparently wpcom blocks access to .json files inside wp-content/languages/.

[anomiex]

Figured it out, and updated the testing instructions so it should be easy for someone else to test it too.

[anomiex]

Sigh. So the wpcom stuff isn't happy because D71392-code isn't merged yet, but it can't be due to p3topS-X5-p2

[anomiex]

Hacked around the wpcom problem, this should be ready for review again.

[github-actions]

Great news! One last step: head over to your WordPress.com diff, D70962-code, and commit it.
Once you've done so, come back to this PR and add a comment with your changeset ID.

Thank you!

[anomiex]

r236678-wpcom