Change language in Thunderbird
To change Thunderbird language, you must first install the Add-on "Quick Locale Switcher". To do this, proceed as follows:
- First, click on the menu button you see on the extreme right edge.
- Select in the drop-down list of "Add-ons".
- Connecting you go on the page "Add-ons Manager" on the "search all Add-ons" and enter in the search field "Quick Locale Switcher".
- The Add is displayed-on in the list, click on the "Install" Button. Start Thunderbird, then restart.
- Many languages such as English, French or Spanish of the "Quick Locale Switcher brings" already missing your desired language, download the language pack easily later down.

Quick Locale Switcher
Another very useful and also very popular Add-on is "Lightning". This add-on enriches Thunderbird with a practical calendar.
