The latest version of synfig 1.5.1 supports .tsv “tab separated values” time/one-of-8-letters files as output by a program called “rhubarb” using the same switch and animation-from-file conversions as are/have-been in place for papagayo. But rhubarb is infinitely less pain in the neck, you just pass a .WAV file through it to get the .tsv out of rhubarb, import that tsv into synfig, and tend to the mouth shapes ABCDEFGX. You also have to import the wav if you want to hear it, and read it again in the sound panel for synchronizing with whatever graphics you may be working with.
Thanks Baaz for doing this. Rhubarb suport 🙃 - #3 by Baaz