The code that JGuiGen generates is internationalized. One of the things that this means is that all visible text (labels, prompts, buttons, error messages, etc.) are written to a text file. These text files are called resource bundles. Each visible items is in the text file as a key=value pair. By making a copy of the resource bundle (and giving it the right name) and translating the "value" portion of the pair, your program can run in a different language.
Here is the resource bundle generated for the UserLogData class.
Here is a sample with some of the items translated to Spanish.
Spanish Resource bundle