Tagging text as being in arbitrary complex-script languages

https://wiki.documentfoundation.org/ReleaseNotes/5.4 says,

"The language list for text attribution now also displays BCP47
language tags provided by dictionaries if a language is not known in
the predefined set of languages. (Eike Rathke (Red Hat, Inc.))

    Such additional language tags are placed in curly brackets /
    braces, for example {en-DK}, and are displayed at the top of the
    list after the [None] entry."

Is some additional information required in the .oxt file for the
dictionary if the script is not "Western text"?  For example, I have
installed a dictionary (of my own devising) for language nod-TH, but it
only shows up (in LibreOffice 6.2.2.2) in the language list for
Western text.  (The language is only written in CTL scripts - Thai
and Lanna.)

The work-around of manually editing the XML of a writer document to
insert the language and country still works.

Richard.