nullgraph
I've been reading vietnamese books on the prs-505 for a couple years. Even after using font hack I could never read epub books correctly.
I end up embedding fonts into epub file. I found this site -
http://fontchu.com/- to be useful with lots of Vietnamese-compatible fonts.
Watch out for fonts with large file size - it does slow down page turning etc. The above site has good fonts with characters relevant to Vietnamese only thus keeping the file size down.
I used Windows character map to ensure that fonts file contains: ấ or ử i.e. multi-symbols over the letters.
I'm still trying to find the "best" font for my eyes
