GiellaLT provides an infrastructure for rule-based language technology aimed at minority and indigenous languages, and streamlines building anything from keyboards to speech technology.
The process of adding languages in LibreOffice is documented here:
Save the resulting xml file in the techdoc/proof/spelling/hfst/locale/ folder.
Thereafter, the new language must be added to LO. Register at https://bugs.freedesktop.org/, and file a bug saying the language is missing, with the xml file as an attachment.