The process of adding languages in LibreOffice is documented here:

* [https://wiki.documentfoundation.org/LibreOffice_Localization_Guide/How_To_Submit_New_Locale_Data]
* [The Locale Generator|http://www.it46.se/localegen/select_lang.php] (for generating new locale data)
* [How to add the new language|https://wiki.documentfoundation.org/LibreOffice_Localization_Guide]

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.