Mbrola extension for mutwo.
mutwo.mbrola is available on pypi and can be installed via pip:
pip3 install mutwo.mbrola
Mbrola has problems with long durations of single phonemes (longer than around 8 seconds). Sometimes it will just produce empty sound files in this case. It is not clear yet what's the border, maybe in the mbrola documentation one can find more about this.