Ubuntu – How to start Firefox in another language than the default

firefoxlocale

I want to temporarily use Firefox in another languages so that menus and everything else in another language. How can I do that?

I have tried

firefox -no-remote -UILocale en-GB

but that still loads Firefox with my default locale (I have en-GB locale for Firefox installed).

Goto menu item Adds-On, then Languages and disable the non wanted language.
You need to restart firefox, then.

Another solution: from command line:

LC_ALL=en_GB firefox -no-remote

in this way you change the environment of firefox, making it believe it is in en_GB locale, only for the given execution.

Obviously both the locale than the firefox support package for that locale should be installed, for this to work.

For example, to see firefox in french, the prerequisites are:

sudo locale-gen fr_FR fr_FR.UTF-8 && echo "Success"
sudo apt-get install firefox-locale-fr
LC_ALL=fr_FR firefox -no-remote

Extra steps to try:

Try:

sudo update-locale LANG="fr_FR.UTF-8" LANGUAGE="fr_FR"
sudo dpkg-reconfigure locales

Perhaps adding LANG and LANGUAGE in /etc/environment could force a change. Try logout/login or rebooting.
locale will show your current locale for the current user. Perhaps it's worth checking out these files just to be sure no local language variables are set: ~/.profile ~/.bashrc ~/.bash_profile

More info:

Firefox seems to use myspell/hunspell and listing /usr/share/myspell/dicts/ shows me the dictionaries that I'm given options to use:

$ ls -1 /usr/share/myspell/dicts/*.dic
/usr/share/myspell/dicts/en_CA.dic 
/usr/share/myspell/dicts/en_GB.dic
/usr/share/myspell/dicts/en_ZA.dic
...

Search for the dictionary filename in installed packages:

$ dpkg -S /usr/share/myspell/dicts/en_CA.dic
hunspell-en-ca: /usr/share/myspell/dicts/en_CA.dic

So with the Canadian language package name, the fix is to remove it:

sudo apt-get remove hunspell-en-ca