The screenshots give a general exposition of the tools and options supported by the extension. Note that the provided toolbar button must be added manually from the toolbar palette to be accessible.
If you have arrived to this page searching how to change the interface language once and for all, the recommended procedure is to download and reinstall the entire application (either Firefox, Thunderbird or SeaMonkey) already translated to your language.
Please note that it's not to manage the preferred languages for the content of webpages, or the language for the spell-checker.
Available in: عربي (ar), Català (ca), Deutsch (de), Dolnoserbšćina (dsb), Ελληνικά (el), English (en-US), Esperanto (eo), Español (es-ES), Français (fr), Gàidhlig (gd), Hornjoserbsce (hsb), 日本語 (ja), 한국어 (ko), Latviešu (lv), Nederlands (nl), Português (do Brasil, pt-BR), rumantsch (rm), Русский (ru), Српски (sr), Svenska (sv-SE), Українська (uk-UA), 中文 (简体, zh-CN), 正體中文 (繁體, zh-TW).
You can help with the localization to other regions at BabelZilla.
About porting it to the WebExtensions (WE) add-on model
Check here the up-to-date development status. Currently, a compat-with-Firefox-57-and-beyond port isn't possible at all.
- Users of language packs in a experimental updates channel (Nightly/Daily and, to a lesser extent, Aurora and Beta) are prone to, after an update of the application or a switch of the preferred language, found a ugly error message at startup or window loading that include the words "...Parsing Error: undefined entity...", and which prevents any further interaction with the application. It's caused by the language pack in use, which is outdated/incomplete. To fix it, force the execution of the application in Safe Mode, and then disable or update the conflicting langpack via the Add-ons Manager.
- Uninstalling this extension doesn't revert the value of any application preference previously changed though it; this shouldn't be considered as a method to "fix" undesired language configurations.
The main icon used by this extension is from the icon theme of the Tango Desktop Project.