[tomsem]

It works for the Latin based script in use today, but probably not the Siniform based script used prior to 20th century. And of course this is just for display, not keyboard input (the latter would require a hack to add vietnamese alphabet to the Sym table).

Text search matches on the latin base character, so it should still be useable with Vietnamese even though you cannot type the word in 'correctly.'

Attached is a screenshot. I can't read Vietnamese but I don't see any obvious problems.