ProcessBook has several language packs that can change the language of the GUI to a localized language. There are 8 languages that are currently available in the latest ProcessBook version.
The part that you probably have to do more work for localization is the content that you add into the displays. There isn't really a feature to localized the contents of PIW and PDI files, you probably need to customize this. Another thing that you want to take note of is that ProcessBook uses the system codepage to encode and decode text content in PIW and PDI files, so this means that there are chances that the text when saved on one computer might end up decoded wrongly on another computer when the region setting is different.
I would invite you to take a look at the "Localization with PI" whitepaper that I have put up on the Library section for more information and other aspects that you can take note of.