If you do some changes in MO/PO files it'll be lost on new update, because MO/PO files are located in plugin folder. If you're updating a translation file or doing a new translation you should send the files to us. We'll update it in core and it'll not be lost on future release. Or you can contribute forum translation here. More info: https://wpforo.com/docs/root/translation/getting-involved-in-translation/