## Summary of the Pull Request
This PR adds a global "language" setting, which may be set to any supported BCP 47 tag.
Additionally a ComboBox is added to the settings UI under "Appearance", listing all languages with their localized names.
This PR introduces one new issue: If you change the language while the app is running, the UI will be in a torn state, as not all UI elements refresh automatically if the `PrimaryLanguageOverride` is changed.
## PR Checklist
* [x] Closes#5497
* [x] I work here
* [x] Tests added/passed
* [ ] Documentation updated. If checked, please file a pull request on [our docs repo](https://github.com/MicrosoftDocs/terminal) and link it here: #xxx
* [x] Schema updated
## Validation Steps Performed
* UI language changes when changing the "language" in settings.json before starting WT / while WT is running. ✔️
* "language" field is removed from settings.json if "Use system default" is selected. ✔️
* "language" field is added or updated in settings.json if any other language is selected. ✔️
* Removes qps- languages if debugFeatures is false. ✔️
* Correctly refreshes all UI elements with the new language. ❌
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