Hi Alexandre,
From what I understand, this would be a matter of adding a font which has those characters to your site so that they render. Since this is a custom font you want to use, that would be something to implement on your end, and not on Publii.
I inspected the page you sent, and it looks like it uses the ‘Dushan Musa Alphabet’. Download that font, install it on your computer, and add it to your website files. Make sure to edit your CSS files so that the font is used. Here’s more info: https://medialoot.com/blog/how-to-use-web-fonts/