Ubuntu Keyboard is the official QML and C++ based keyboard plugin for Ubuntu Touch. We follow an open source model where the code is available to anyone to branch and hack on.
If the source material used for presage prediction models is updated, the
databases can be regenerated by running make lang_db_$lc within the plugin's
src directory (where $lc is the language code for the updated language,
e.g. make lang_db_en for English)
The easiest way to build this is using crossbuilder by simply running:
crossbuilder
See crossbuilder on github for details.
Here are some useful links with regards to the keyboard plugin development.