Qt's own translations / difference between qt_*.qm and qtbase_*.qm

I couldn't find it in the docs: What is the difference between qt*.qm and qtbase_*.qm?
Which ones of Qt's own translation files am I supposed to include for my application?
Thank you!

Edit:
I've looked at the file sizes and got the impression that they were modularized (for Qt5?). But some languages aren't (I'm on Qt 5.2).

I now load qtbase_* on Linux and everything works correctly.
But on Windows, the translations for QMessageBox::Yes and ...::No are missing. I don't know why.
Other Qt translations (for example, the context menu in a QTextEdit) are working fine.
Do you have any idea what the problem might be?

A happy new year to all of you. :)