Comment 1 for bug 509248

This also affects me. I have the thunderbird-locale-en-gb and myspell-en-gb packages installed. Thunderbird shows the language pack correctly installed under 'Tools > Add-ons > Languages'. However, I am only able to select the United States English dictionary when composing email.

Current package versions (Lucid):
thunderbird: 3.0.4+nobinonly-0ubuntu1
thunderbird-locale-en-gb: 1:3.0-0ubuntu2
myspell-en-gb: 1:3.2.0-2ubuntu2

This problem is caused by Thunderbird not correctly linking the myspell dictionaries into '/usr/lib/thunderbird-3.0.4/dictionaries/'. I believe there are two possible solutions to this problem:

1) Link Thunderbird's dictionaries directory to the myspell dictionaries directory. This is the solution currently used by Firefox:
  '/usr/lib/thunderbird-3.0.4/dictionaries -> ../../share/myspell/dicts'
  c.f. '/usr/lib/firefox-3.6.3/dictionaries -> ../../share/myspell/dicts'.

2) Link the individual dictionaries at the thunderbird-locale level. This would probably entail making the locale package dependant on the appropriate myspell dictionary pack, e.g.:
  thunderbird-locale-en-gb:
    Depends: myspell-en-gb

  '/usr/lib/thunderbird-3.0.4/dictionaries/en-GB.dic -> ../../../share/myspell/dicts/en-GB.dic'
  '/usr/lib/thunderbird-3.0.4/dictionaries/en-GB.aff -> ../../../share/myspell/dicts/en-GB.aff'.