I'm running the latest FBreader (0.12.0) on Ubuntu. Dutch is indeed listed there as a language. However if I turn Dutch as default on, hyphenation is still not working. Even if the metadata inside the epub is configured as Dutch.
A samplefile of a Dutch newspaper can be found here: http://epaper.nrc.nl/downloads/nrc_20090909.epub
With English or German epub's hyphenation is working normally.
On the latest FBreader on my Pocketbook, Dutch is not listed as an option by the way.