Radek Sidun is publishing The Manual of Diacritics. He writes:
With a few exceptions, the drawback of literature devoted to diacritics is that they are predominantly textual and often lack sufficient illustrations. Because most of us work visually, a textual description of how something should be correctly done and how the result should look is not very helpful. Examples should primarily be shown, specific approaches visualised and clearly demonstrated. This is why, instead of complicated descriptions of the problems associated with diacritics, I chose to put together a set of clear visual examples of possible solutions. To achieve this, I completely redesigned all accents from scratch. The result is 15 typefaces with a new diacritical set designed by me.
The book includes 33 languages. I would love to see his process and approach for redesigning all the accents. Unfortunately, Vietnamese is not included.