Dialoge in Act 5 not read out loud

Since I have arrived in Act 5, the dialoge I find doesn't get read out loud anymore once I click on them. The dialoge from the NPCs in the Overseeer's Tower however, is still read out loud, just not in the parts of the map after that.

This however only applies to the books found thoughout the levels. the NPCS still are vocal.

I don't know if this is a bug or if there just aren't voice-lines for it.


Edit:
I reached act 6 and still the books I find do not seem to read the texts out loud. The characters however do.