src/vs/editor/common/model/tokenizationTextModelPart.ts/TokenizationTextModelPart/setLanguageId
class TokenizationTextModelPart:	public setLanguageId(languageId: string): void {
		if (this._languageId === languageId) {
			// There's nothing to do
			return;
		}

		const e: IModelLanguageChangedEvent = {
			oldLanguage: this._languageId,
			newLanguage: languageId
		};

		this._languageId = languageId;

		this.bracketPairsTextModelPart.handleDidChangeLanguage(e);
		this._tokenization.handleDidChangeLanguage(e);
		this._onDidChangeLanguage.fire(e);
		this._onDidChangeLanguageConfiguration.fire({});
	}