Places of interest may be: 1. Settings for language translator. Most of settings don't need to be written in C code and may be set in language settings file cmn. 2. Settings for phonemes 3. Pronunciation rules in zh_list and zh_rules files.

It would be nice, if you would update documentation (e.g. setup steps/howto for tonal languages) with results of your investigation, to make life easier for other contributors.