The extension is intended for checking grammar using LanguageTool (http://www.languagetool.org/
) facilities (in particular, the extension uses its webserver). Though it can work without any further customization, it is strongly recommended to setup local LT server (see http://nuald.blogspot.com/2009/10/thunderbird-grammar-checker-extension.html
), and change the extension settings to correspond with your server. By default, the extension uses the small-scale server, which can't handle enormous load (and of course, it is not so suitable from privacy point of view).
Supported languages: English (en), Dutch (nl), French (fr), German (de), Icelandic (is), Italian (it), Lithuanian (lt), Polish (pl), Romanian (ro), Russian (ru), Slovak (sk), Slovenian (sl), Spanish (es), Swedish (sv), Ukrainian (uk).