I need to use Pali characters which has been already subset in some Thai fonts but there is not a choice of Pali in Characters/Paragraphs dialog box. So currently I have to put “:lang=pi” into the Fonts drop-down instead. Although it works well but it is not intuitive for common users. Or I can select Sanskrit instead and get the same glyph displayed but its context will be wrong.
Is there good way to get it right?
Thanks.
Read these guidelines. Feature requests are off-topic here. File one at Bugzilla.
Just for the reference: as you certainly know, Pali is a multi-script language and is already listed as Pali Latin for Western text font language in the character dialog.
Thank you for your information. I know that it is multi-script language but I did not know there is “Pali Latin” in the Western Font - Language List before. However I tried it without success.
Now I am consider this question as a new feature request and will put it at Bugzilla.
Sorry for misuse of this place. 
tried it without success.
Why/what did not succeed? What script do you use actually? Why not Latin?
By the way, you might want to read this topic: Is it possible to create a Pāli dictionary for Libreoffice?
Thanks for your concern. Pali is verbal-only (multi-script) language. I need to use Pali Glyph subset of Thai Characters. So it cannot be Latin.
And as erAck replied below that the new choice I mentioned would not solve the problem also. I will find the other work around. (Actually there are some workarounds other ones made up in the past decade but almost of them ruin the integrity of contents. So I am trying to find the better way.)
Many thanks! I got many useful information from you all.
See Request a new language/locale to be added in the wiki.
However, if the language-script is not a Right-To-Left (RTL) or other Complex-Text-Layout (CTL) writing system then you can always enter a BCP 47 language tag in the Western language list’s combo edit box to properly attribute the text portion. In the case of Pali that seem to be several different possible scripts, see Pali - Wikipedia, so it could be pi-Brah for Brahmi or pi-Sinh for Sinhala script, for example (if these are not CTL, I didn’t investigate, at least they ar enot RTL), which then would show up as {pi-Brah} or {pi-Sinh} on top of the language list. Your example of Thai script would not work because Thai is CTL, Sanskrit the same. Unfortunately this free-form language tag is not possible yet for RTL or CTL writing systems.
Note anyway, that the mere presence and selection of a language tag does not preselect fonts matching the alphabet or script.
Thank you for your informative answer.
The new choice “Pali Thai” has been added. It will be available in LibreOffice 7.2.0
(refering to https://bugs.documentfoundation.org/show_bug.cgi?id=139607).
It helps LibreOffice choose a matched glyph for a Pali character in case the font has language substitution (GSUB) set for Pali.