i18n: missing translations in many parts of the admin interface

### Impacted plugin

Jetpack

### Quick summary

Many parts of the Jetpack admin interface do not display translations, even for languages that are fully translated

### Steps to reproduce

1. Install and activate Jetpack on a site running WordPress in English.
2. Go to Settings > General
3. Switch the site language to Russian, [a language that is 100% translated right now](https://translate.wordpress.org/projects/wp-plugins/jetpack/stable/)
4. Go to Dashboard > Updates, and click the button to update translations
5. Ensure that there are no pending translation updates left:

6. Go to Jetpack > Settings or Jetpack > My Jetpack.
=> Note that brand names are not translated, as expected

7. On the Jetpack > My Jetpack page, only some of the strings are translated

8. On the Jetpack > Settings page, only some of the strings are translated

### Site owner impact

Between 20% and 60% of the total website/platform users

### Severity

Major

### What other impact(s) does this issue have?

No revenue impact

### If a workaround is available, please outline it here.

_No response_

### Platform (Simple and/or Atomic)

Self-hosted, Atomic

Start by reproducing the issue in a self-hosted or Atomic WordPress site with Jetpack active, switching the site language to Russian and updating translations. Compare Jetpack > My Jetpack and Jetpack > Settings with the completed Russian translation set; done means translated strings display in both admin pages while brand names remain untranslated.

Written by the indexing model from the issue text.