src/vs/workbench/contrib/localizations/browser/localizations.contribution.ts/LocalizationWorkbenchContribution/isLanguageInstalled
class LocalizationWorkbenchContribution:	private isLanguageInstalled(language: string | undefined): Promise<boolean> {
		return this.extensionManagementService.getInstalled()
			.then(installed => installed.some(i =>
				!!(i.manifest
					&& i.manifest.contributes
					&& i.manifest.contributes.localizations
					&& i.manifest.contributes.localizations.length
					&& i.manifest.contributes.localizations.some(l => l.languageId.toLowerCase() === language))));
	}