getSourceLanguages(mPropertyBag) {
			// TODO: cache the request & invalidate it in case of a writing operation
			return _getWriteConnectors()
			.then(_executeActionByName.bind(undefined, "translation.getSourceLanguages", mPropertyBag));
		}
Gets the source languages for the given application.

@param {object} mPropertyBag - Property bag
@param {sap.ui.fl.Layer} mPropertyBag.layer - Layer
@param {string} mPropertyBag.reference - Flexibility reference
@returns {Promise} Resolving after the languages are retrieved;
rejects if an error occurs