getSourceLanguages() {
				return Promise.reject("translation.getSourceLanguages is not implemented");
			}
Interface called to get the source languages for the given application

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