"Wrong affix file formate for flag" while loading dictionaries from LibreOffice in PostgreSQL 9.3
So I found the answer for Debian at least. 
Hunspell is the successor of Myspell, and they ship with your distribution (in my case Debian).  These are the dictionaries you can use.  You can install these by executing

apt-get install hunspell-en-us


These dictionaries are installed in /usr/share/hunspell or /usr/share/myspell. The PostgreSQL dictionaries that are automatically generate out of these file when installing through apt-get are located in /var/cache/postgresql/dicts. Furthermore apt-get automatically creates links to the files generated in you /usr/share/postgresql/VERSION/tsearch_data dir. In short you are ready to use them.

If you want to manually install hunspell or myspell dictionaries you can place them in the /usr/share/hunspell or /usr/share/myspell dirs. And execute 

pg_updatedicts


This will generate PostgreSQL compatible dictionaries in

/var/cache/postgresql/dicts


and you will have to link them yourself /usr/share/postgresql/VERSION/tsearch_data

ln –s /var/cache/postgresql/dicts/de_de.affix           \
  /usr/share/postgesql/VERSION/tsearch_data/            \

ln –s /var/cache/postgresql/dicts/de_de.dict            \
  /usr/share/postgesql/VERSION/tsearch_data/            \