src/vs/workbench/contrib/localization/electron-sandbox/localeService.ts/NativeLocaleService/setLocale
class NativeLocaleService:	async setLocale(languagePackItem: ILanguagePackItem): Promise<boolean> {
		const locale = languagePackItem.id;
		if (locale === language || (!locale && language === 'en')) {
			return false;
		}
		const installedLanguages = await this.languagePackService.getInstalledLanguages();
		try {

			// Only Desktop has the concept of installing language packs so we only do this for Desktop
			// and only if the language pack is not installed
			if (!installedLanguages.some(installedLanguage => installedLanguage.id === languagePackItem.id)) {

				// Only actually install a language pack from Microsoft
				if (languagePackItem.galleryExtension?.publisher.toLowerCase() !== 'ms-ceintl') {
					// Show the view so the user can see the language pack that they should install
					// as of now, there are no 3rd party language packs available on the Marketplace.
					const viewlet = await this.paneCompositePartService.openPaneComposite(EXTENSIONS_VIEWLET_ID, ViewContainerLocation.Sidebar);
					(viewlet?.getViewPaneContainer() as IExtensionsViewPaneContainer).search(`@id:${languagePackItem.extensionId}`);
					return false;
				}

				await this.progressService.withProgress(
					{
						location: ProgressLocation.Notification,
						title: localize('installing', "Installing {0} language support...", languagePackItem.label),
					},
					progress => this.extensionManagementService.installFromGallery(languagePackItem.galleryExtension!, {
						// Setting this to false is how you get the extension to be synced with Settings Sync (if enabled).
						isMachineScoped: false,
					})
				);
			}

			return await this.writeLocaleValue(locale);
		} catch (err) {
			this.notificationService.error(err);
			return false;
		}
	}