15035: Missing I18N in UI

[CamilleLetavernier]

What it does

• Localize some commands and texts that were missing

Note: the original issue contains a long list of commands that were previously not localized. Localizations are generated quite late in the release cycle, so they have been introduced just yesterday morning. Only a few localize calls were actually missing from the code base; so I added them.

How to test

The PR only introduces nls.localize() calls, so it can't immediately be tested. I'm not sure what is the best way to test the changes, but what I did:

• Add (a subset of) the keys to your favorite language, in packages/core/i18n/nls.**.json

For example, in French:

"theia": {
    "core": {
      "about": {
          "listOfExtensions": "Liste des extensions"
      }
    }
}

• Start Theia
• In the Command Palette, call Configure Display Language and select the modified language
• Restart Theia Frontend
• Check that the localized messages properly appear (For this example: open the "About" dialog)

Follow-ups

• Wait until all keys are officially localized (Typically done just before release)

Breaking changes

• This PR introduces breaking changes and requires careful review. If yes, the breaking changes section in the changelog has been updated.

Attribution

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines