src/vs/editor/common/services/modelService.ts/ModelService/_onDidChangeLanguage
class ModelService:	private _onDidChangeLanguage(model: ITextModel, e: IModelLanguageChangedEvent): void {
		const oldLanguageId = e.oldLanguage;
		const newLanguageId = model.getLanguageId();
		const oldOptions = this.getCreationOptions(oldLanguageId, model.uri, model.isForSimpleWidget);
		const newOptions = this.getCreationOptions(newLanguageId, model.uri, model.isForSimpleWidget);
		ModelService._setModelOptionsForModel(model, newOptions, oldOptions);
		this._onModelModeChanged.fire({ model, oldLanguageId: oldLanguageId });
	}