Thanks for your fast response.
I have both directories.
/usr/share/myspell/dicts is used by:
hyphen-ca, myspell-en-gb, myspell-en-us, hyphen-en-us, mythes-en-us, mythes-ca
/usr/share/hunspell is used by:
myspell-es, myspell-en-gb, myspell-en-us, myspell-ca
I found that working spelling packages using both directores place a symlink from /usr/share/myspell/dicts to the real files /usr/share/hunspell. For instance:
lrwxrwxrwx 1 root root 24 Jul 9 2012 /usr/share/myspell/dicts/en_GB.aff -> ../../hunspell/en_GB.aff
lrwxrwxrwx 1 root root 24 Jul 9 2012 /usr/share/myspell/dicts/en-GB.aff -> ../../hunspell/en_GB.aff
lrwxrwxrwx 1 root root 24 Jul 9 2012 /usr/share/myspell/dicts/en_GB.dic -> ../../hunspell/en_GB.dic
lrwxrwxrwx 1 root root 24 Jul 9 2012 /usr/share/myspell/dicts/en-GB.dic -> ../../hunspell/en_GB.dic
If the path in texworks is hardcoded to /usr/share/myspell/dicts/ , then I can solve the problem by symlinking. I tested this and it works. Now spanish is available.
However, I'm not sure if the bug is due to texworks uses only one directory (since other editors seem to use several, because they do not require the symlink) or the bug is in myspell-es because it does not symlink on install.
Thank you very much,
Salva