Some pages on ban.wikipedia use the Bali script but I'm told that most users don't have the required font on their device. We can add the Noto font for Balinese to webfonts.
I've installed google-noto-serif-balinese-fonts-20181223-6 and it works. I can't read Bali so I can't tell how good it is but it seems people use it without big issues and that the author of the (non-free) Vimala font has been tasked with improving it further.
This task is only about adding the font, not necessarily about enabling it on ban.wikipedia. We should however at least enable it on wikisource.org so that we're ready to welcome Bali script pages in it.