I get it to work with LibreOffice, which seems to call it through Python, and I haven't checked how it's called exactly.
Anyway, in QPicoSpeaker it works too - although with a little fiddling, which may be just glitches in the GUI - but in Orca it's silent entirely.
For your reference, here's the relevant lines in
#AddModule "espeak-ng" "sd_espeak-ng" "espeak-ng.conf"
#AddModule "pico-generic" "sd_generic" "pico-generic.conf"
#LanguageDefaultModule "en" "pico-generic"
The "espeak-ng" module line has never been uncommented, and "espeak-ng" doesn't have a language line. Otherwise I uncomment either only the DefaultModule line for espeak-ng, or both the DefaultModule line for pico-generic and the LanguageDefaultModule line for pico-generic.
Doing this, pico-generic does not produce sound and espeak-ng does. It's a bit strange to me, but I'll dig more into it