I believe it requires the installation of speakup.
Here is some info on installing speakup modules into the Linux kernel.
Hopefully, someone else has easier info on this.
I found pure Debian easiest on installing speakup, but I have to admit I often got confused and used the easier method of purchasing voxin and installing from Gilles Casse's excellent scripts.
Voxin is very reasonably priced and so far all updates have been free.
Each includes voxin and also vocalizer embedded.
Sample the voices to see what you need.
Compact versions require less computer power.
I am very pleased with voxin and vocalizer embedded high. They sound very natural even at high speeds that blind users are apt to use on long texts.
Kind regards,
David Ring