Translation:His stories were so sad that people mocked him.
Sorry for my non understanding. I am not native English.
If you think that the translation of the Esperanto sentence with "oni" should be accepted as «His stories were so sad that people mocked him.» and as «...that one mocked him.» and as «...that they mocked him.», then please report this as error. Always report errors if you are sure
I dont understand your problem. The displayed sentences below are : « Liaj rakontoj estis tiel malĝojaj, ke oni mokis lin. His stories were so sad that people mocked him ». So there is already "oni". Maybe you made another error. You can always report errors if you are sure. Duo will checkt your report and correct or not.