Since V3 its very easy to change/translate all labels used in the product designer. All labels(texts) are stored in a separate JSON file, which is located in the lang folder of the example. Just open default.json and start editing all labels. Do not change the keys!
If you want to change the location of the JSON or the filename, you have to enter the correct file URL for the plugin. You can easily change the URL via the langJSON option in the plugin options. This option receives the URL as string or a JSON object containing all content from the language JSON file (default.json).