1. Install the language pack from the following page. Verify that it shows up in the Add-ons Manager, Languages category.
   • https://addons.mozilla.org/firefox/language-tools/
2. Type about:config into the address bar and press Enter.
3. To bypass the warning, press the big button labeled "I'll be careful, I promise!".
4. In the search box, paste intl.locale.matchOS
5. In the search results, make sure intl.locale.matchOS is set to false — double-click it to toggle its status.
6. In the search box, paste general.useragent.locale
7. In the search results, double-click general.useragent.locale and set its value to the ISO 639-1 language code. For Romansh, that's rm
8. Restart Firefox for the change to take effect.

You can also change the interface language with an add-on like Locale Switcher.

• https://addons.mozilla.org/firefox/addon/locale-switcher/

Thank you very much for your fast answer. But unfortunately it didn't work. I've already tried this before and now again: It doesn't work. Did it work for you? Have you tried these steps? The add-on is installed, general.useragent.locale is set to "rm", but the UI is still german... (And: Yes, I restarted Firefox)

Do you have the Firefox version from the Mozilla server or one provided by your Ubuntu distribution.

You can try to create a "/distribution/bundles" folder in the Firefox installation folder and install the language pack(s) in that folder.

• /questions/984445 How do I install a language XPI globally and make it the default language?

This is a bit more tricky and you also won't be able to update the language automatically when Firefox updates.

You need to create a folder with the ID of the language pack in the /distribution/bundles folder and extract all the files in the XPI (ZIP) archive this folder.

• /distribution/bundles/langpack-rm@firefox.mozilla.org

Thank you for your answer. My Firefox version is provided by my Ubuntu distribution. I tried to follow the steps you indicated. I created a folder called "bundles" with a subfolder called "langpack-rm@firefox.mozilla.org" containing all the files I extracted from "rumantsch_language_pack-28.0-fx.xpi". After this I tried to move the folder to usr/lib/firefox/distribution, which failed. So I started Nautilus from the terminal with "sudo nautilus". After this I was able to move the folder.

Now there is a directory like this: /usr/lib/firefox/distribution/bundles/langpack-rm@firefox.mozilla.org/ containing the stuff from the xpi.

But the terminal is full of errors like "** (nautilus:7618): WARNING **: nautilus_canvas_view_remove_file() - directory not canvas view model, shouldn't happen. file: 0x1615960:file:///usr/lib/python2.7/htmlentitydefs.py, dir: 0x9a66a0:x-nautilus-search://0/, model: 0xb0ba40:file:///usr/lib, view loading: 1 If you see this, please add this info to http://bugzilla.gnome.org/show_bug.cgi?id=368178"

And Firefox still speaks german...

Would it be easier to solve this problem if I install the Mozilla provided version of Firefox? How can I install it?

You can find the full version of the current Firefox 28.0 release in all languages and for all Operating Systems here:

• http://www.mozilla.org/en-US/firefox/all.html

See also:

• http://kb.mozillazine.org/Installing_Firefox#Linux

Thank you very much. This works!

Unfortunately it's not too user-friendly... Do I have to install updates manually? Is there a way to install a specific language version (like rumantsch) using a repository?

Firefox will be updating to Fx29 with the next few days. ( Tuesday 29th April )

The Mozilla builds of Firefox on Ubuntu should attempt to download and update themselves. Once the updates are available check by using

• Help -> About Firefox
  • Assuming your Firefox is set to upgrade (That is the default)
    Edit -> Preferences -> | Advanced| -> | Update |
    Advanced panel - Accessibility, browsing, network, updates, and other advanced settings in Firefox_update-tab

Davent wrote:

general.useragent.locale is set to "rm", but the UI is still german...

On Linux, you also need to set intl.locale.matchOS to false

• https://bugzilla.mozilla.org/show_bug.cgi?id=542999

It works! Great. Thank you, Gingerbread Man and cor-el!