When I want firefox to read text from a site, I get following message
Your operating system does not have a text-to-speech voice for the current language (nl-NL). Please install the missing language pack, restart your browser, and try again.
I use Manaro KDE
This might be helpful:
What Firefox add-on are you using to read the text? I just installed Read Aloud: A Text to Speech Voice Reader – Get this Extension for Firefox & it had no issues reading this thread, and another thread in the Nederlands section of this forum. I didn’t have to install any special language packs or TTS software on my system.