Add Vietnamese glyphs
To get all the Latin diacritics necessary for writing Vietnamese into your font, simply switch to the Font view (Cmd-Opt-1). In the left sidebar, make sure Languages > Latin is expanded. There you will find a category Vietnamese. Right click to open a list of all the missing glyphs. Select them all and click on Generate.
The accents that make our lives difficult in terms of font technology, are the double accents with circumflex and breve: they can have a tilde, a hook, an acute or a grave on top of them. The problem is, they can rise really high above the cap height. And if they do, you may need to readjust the vertical metrics of your font in order to avoid clipping wherever possible.
In principle, i
One solution may be to devise a flatter alternate
Another solution, that can build on top of the flat circumflex, involves mark ligatures.<
top_viet anchor: mekkablue script