Changes
→Silent installation of dictionaries (spell-checking)
Mozilla Thunderbird keeps the dictionaries in <code>%PROGRAMFILES%\Mozilla Thunderbird\components\myspell\</code>.
By default, it only has English dictionary(for [http://weblogs.mozillazine.org/ben/archives/016618.html licensing reasons].
Installing a new dictionary is simple - just copy the dictionary files for a given language to that folder.