Hello Klaus,
thank you for using my plugin.
This problem is related to Loco translate plugin, not to WSB Brands, but I can try to help:
When you create new translation using Loco, you should NOT use “Author” folder as location to save the translation files. Use “Other” location instead. Translation files in author location are overwritten with every plugin update. So if you want your custom translation to be permanent, just save it to “Other” location (i.e. “Loco” folder). Note that you can have two or more translations (in different folders), but Loco will use the one from its own folder first. Hope it helps!