include vietnamese in diacritics decomposition line

Test multiple combining marks with a sentence containing various accents from
<http://lists.hanoilug.org/pipermail/du-an-most/2011-December/005228.html>
(apparently a common saying).

Replace latvian by a shorter variant from <http://clagnut.com/blog/2380/>,
with unneeded adjectives (brīvi, celofāna) omitted to fit.