I'm not sure if I understand your question well.
Do you want a tool to translate one language to another, like Google Translate, or do you want to translate all of the text and strings of your application objects?
Powerbuilder comes with a Translation Toolkit and Translator tool. This should generate all entries of text attributes in your application to a database. It's been years since I've last used it. Maybe it's what you're looking for.
As mentioned by Mike, there's this "Enable" product. A much more advanced and expensive version of what the kit does which comes with Powerbuilder.
regards,
MiguelL
Maybe there's others who offer an API.