I really don't know
You should ask in their Github page
Maybe ask for this new feature or some info on where to write the syntax definition...
Thanks for the downvote, you made me learn a new thing. I followed my own suggestion and went to their Github page (as I said could be the best way to get an answer) and looked for people asking for new language support. Normal stuff right?. Found a post of a person asking for "Language Support for Ren'Py"
There, a person who has the know-how of code's environment, told him and us that code uses
So I went to the old Google, searched for
"twig gtksourceview" and found this:
https://twig.symfony.com/doc/2.x/templates.html (I believe this is the Official website of the language?)
If we look for
gtksourceview we find
,that leads us to:
To add support to others just repeat:
Go to the official website and look for their gtksourceview template
format file, if they don't have a template made, look for it in Google and if all goes wrong you just can edit/create one yourself. (see below for format definition)
Create it or download it
Save it in your system where it should (see below)
Where to save it?