Email, Messaging, & Video Calls Email How to Add a Dictionary to Mozilla Thunderbird Spell Check Define custom spell check settings for your email by Heinz Tschabitscher Writer A former freelance contributor who has reviewed hundreds of email programs and services since 1997. our editorial process Heinz Tschabitscher Updated on April 30, 2020 Email Yahoo! Mail Gmail Tweet Share Email Your Mozilla Thunderbird's spell check may only be limited to finding fault with your English, regardless of whether you compose your emails in Arabic, English, French or even Icelandic. Given how useful spell checking can be especially with languages other than the language you grew up speaking, Mozilla Thunderbird should really be able to learn new tongues and fortunately, it can. All it needs is the proper dictionary. Add a Dictionary to the Mozilla Thunderbird Spell Check To install a new language for the Mozilla Thunderbird spell checker: Select Edit > Preferences from the menu in Mozilla Thunderbird. Open the Composition category. Go to the Spelling tab. Select Download More Dictionaries. Follow the Download Dictionary link for the desired dictionary. A Thunderbird add-on page will open for your dictionary. Press Add to Thunderbird. Wait for the download to finish; even if nothing seems to be happening, chances are a dialog will eventually appear. Press Add when asked to confirm the installation. When it's done, Thunderbird will display a message letting you know that the dictionary was added successfully. Add a Dictionary to the Mozilla Thunderbird Spell Check in Mozilla Thunderbird 2/3 To install a new spell checking dictionary in Mozilla Thunderbird 2 and 3: Open Mozilla Thunderbird. Select Tools > Add-ons from the menu. Open your browser. Go to the Mozilla Thunderbird dictionaries page. Follow the Download Dictionary link for the desired language. Drag and drop the desired Download Now link to Mozilla Thunderbird's Add-ons window. Switch to the Add-ons window. Press Install Now in the Software Installation dialog. Now press Restart Thunderbird. You can use the new dictionary by selecting it from the Spell drop-down menu (select the down arrow) while composing a message.