Ensure correct translation loading when loading assets via CDN

[akirk]

When activating the CDN, the Jetpack blocks don't load their translations properly. This is because Core language loading assumes local files. This fixes the paths under the hood before the JSONs are loaded.

Testing instructions:

1. Change your UI language to something other than English (with sufficient translation percentage, e.g. German, Spanish, or French).
2. Activate Jetpack CDN in the Jetpack Settings.
3. Create a new post with the Gutenberg editor.
4. Click "Add New Block" and scroll down to the Jetpack blocks. Block names and descriptions should be translated.

Proposed changelog entry for your changes:

• Fixed Translation loading of Gutenberg blocks with activated CDN.

[akirk]

The hairy thing here is that we need to rewrite only the plugin translations. It looks like core assumes that these CDN-ed plugins have their translations in the core folder and not in the plugins folder.

[jetpackbot]

Thank you for the great PR description!

When this PR is ready for review, please apply the [Status] Needs Review label. If you are an a11n, please have someone from your team review the code if possible. The Jetpack team will also review this PR and merge it to be included in the next Jetpack release.

Scheduled Jetpack release: March 3, 2020.
Scheduled code freeze: February 25, 2020

Generated by 🚫 dangerJS against 434cf50

[kraftbj]

This worked well for me. If testing, be sure to have your translations packages fully updated and you're dropping the PHP on a stable version of the plugin so the CDN would fire for the assets.

[jeherve]

This works well on my end as well. Merging.