Hey, so as you know Vietnamese has two main input schemes, Telex and VNI. I think for any layout design endeavor to be successful in Vietnamese, it should be based on one of these two. I've seen the Colemak community flirt with the idea of integrating Vietnamese input, but the layout itself felt a bit too English-centric (e.g. the NH digram is awful), not to mention the fact that they preferred using dead keys as opposed to character composition. Here's the
VNI layout for reference, note the keys WZFJ are practically unused in VNI.
The optimizations I did a few months ago focused on finding the optimum between Telex and standard English, which performed well enough against vanilla Colemak and surprisingly a close match with MTGAP. For starters, you can find the
converter script on my repo which strips the diacritics from e.g. "bánh mì" to "banhs mif".
Another thing that's on my mind, is that whether a layout optimized for 20 languages would look or perform better than one that is optimized only for a pair of languages. The author of AdNW mentioned the Pareto optimum could only go as
bad as the sum of the two languages, so I'm a bit skeptical about the practicality of such a layout. Regardless, good luck my friend!