Another aspect of software internationalization that pseudo-localization can test is whether all relevant resources have been made localizable.
Now, I understand that in order for this test to work, everything that is shown to the user must be visually inspected. This means the entire fixed user interface must be made to display, including windows that come up when various menu options are selected, pop-up windows, help messages, alternate text, user messages, and, that most difficult of entities to bring to view, error messages.
It's funny, when I tell people pseudo-localization can test 9 aspects of internationalization (actually I started with 5 and found more as time went on), this is the test they claim is not valid. And yet, at the same time, this aspect is the primary one that people claim they are testing when they pseudo-localize their product. Go figure. Personally I'm not confident that you can verify the entire user interface has been properly externalized this way, only a good portion of it, and therefore likely all of it. The key word is likely.
So run your pseudo-localization tool, bring up the product (hopefully it picks up the pseudo-localized resources - see the previous post), and have a good look. Try to create some errors so you can at least check that some error messages are being picked up correctly. In case you're wondering, you're checking for text that is still in the source language, without the additional characters or character transformations that the pseudo-l10n creates.
And then, move on to the next test.