Fix Could not fetch translation json for locale: 'de'

[Nils1729]

Fixes #1419.

Checklist

• [x] Ensure your code works with manual testing
• [ ] Linter and other CI checks pass
• [x] Sign-off given on the changes (see CONTRIBUTING.md)

In implementation it turned out that it was the opposite problem than in the comment: There is no generic de, only the specific de_DE. I tried to cover this case as generically as possible, although it only occurs with en and de at the time of writing.

Type: defect

[Nils1729]

I am not really happy with the amount of logging, as every locale that cannot be found produces a stack trace like this:

Changing application language to de
Fetching translation json for locale: de
Could not fetch translation json for locale: 'de' Error: Cannot find module './i18n/strings/de.json'
Require stack:
- /opt/Element/resources/app.asar/lib/language-helper.js
- /opt/Element/resources/app.asar/lib/tray.js
- /opt/Element/resources/app.asar/lib/settings.js
- /opt/Element/resources/app.asar/lib/ipc.js
- /opt/Element/resources/app.asar/lib/electron-main.js
- 
    at node:internal/modules/cjs/loader:1084:15
    at Function._resolveFilename (node:electron/js2c/browser_init:2:116646)
    at node:internal/modules/cjs/loader:929:27
    at Function._load (node:electron/js2c/asar_bundle:2:13327)
    at Module.require (node:internal/modules/cjs/loader:1150:19)
    at require (node:internal/modules/cjs/helpers:121:18)
    at AppLocalization.fetchTranslationJson (/opt/Element/resources/app.asar/lib/language-helper.js:96:20)
    at /opt/Element/resources/app.asar/lib/language-helper.js:109:39
    at Array.filter (<anonymous>)
    at AppLocalization.setAppLocale (/opt/Element/resources/app.asar/lib/language-helper.js:108:86) {
  code: 'MODULE_NOT_FOUND',
  requireStack: [
    '/opt/Element/resources/app.asar/lib/language-helper.js',
    '/opt/Element/resources/app.asar/lib/tray.js',
    '/opt/Element/resources/app.asar/lib/settings.js',
    '/opt/Element/resources/app.asar/lib/ipc.js',
    '/opt/Element/resources/app.asar/lib/electron-main.js',
    undefined
  ]
}
Fetching translation json for locale: de_DE
Resetting the UI components after locale change

This only affects en and de. But a stack every time Element launches with one of these locales clutters the journal with non-errors. On the other hand, these missing locales might be errors sometimes. To the reviewer: Is just logging everything acceptable? What are the alternatives?

[Nils1729]

Drafting this because it is not critical and seems rather complex. I'll come back once I have some more time at hand.