src/vs/editor/common/services/languageService.ts/LanguageService/_createAndGetLanguageIdentifier
class LanguageService:	private _createAndGetLanguageIdentifier(languageId: string | null | undefined): string {
		if (!languageId || !this.isRegisteredLanguageId(languageId)) {
			// Fall back to plain text if language is unknown
			languageId = PLAINTEXT_LANGUAGE_ID;
		}

		if (!this._encounteredLanguages.has(languageId)) {
			this._encounteredLanguages.add(languageId);

			// Ensure tokenizers are created
			TokenizationRegistry.getOrCreate(languageId);

			// Fire event
			this._onDidEncounterLanguage.fire(languageId);
		}

		return languageId;
	}