Recent answers to can't change the language of the user interface with "general.useragent.locale" after auto update Nov 18https://support.mozilla.org/en-US/questions/11473542016-12-09T09:13:09-08:00Note that you can also use a command line switch to start Firefox with a specific locale if you have2016-12-09T09:13:09-08:00cor-elhttps://support.mozilla.org/en-US/questions/1147354#answer-942963<p>Note that you can also use a command line switch to start Firefox with a specific locale if you have multiple locales installed.
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<ul><li><a href="https://developer.mozilla.org/Command_Line_Options" rel="nofollow">https://developer.mozilla.org/Command_Line_Options</a>
</li></ul>
<p>You can create a desktop shortcut with the "-UILocale xx-xx" switch appended to the command line to start Firefox with a specific locale.
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<ul><li>Start &gt; Run: firefox.exe -UILocale en-US
</li></ul>Glad it worked in the end {Use Firefox in another language} & thanks for letting us know.
Note i2016-12-08T19:17:48-08:00John99https://support.mozilla.org/en-US/questions/1147354#answer-942845<p>Glad it worked in the end {<a href="/en-US/kb/use-firefox-another-language" rel="nofollow">Use Firefox in another language</a>} &amp; thanks for letting us know.
</p><p>Note if you want only one specific language it is often best just to pick that Firefox version and install it. (Pick from <a href="https://www.mozilla.org/firefox/all/" rel="nofollow">https://www.mozilla.org/firefox/all/</a> no need to explicitly uninstall the original version, and certainly avoid using any third party uninstaller)
</p><p>If you change over frequently then find a suitable language manager add-on, or possibly consider setting up separate Windows accounts, or separate Firefox profiles for other users.
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<ul><li> Add-on <a href="https://addons.mozilla.org/firefox/search/?q=language+switcher+manager&amp;appver=50.0&amp;platform=windows" rel="nofollow">Search</a> -&gt; examples
<ul><li> <a href="https://addons.mozilla.org/firefox/addon/quick-locale-switcher/" rel="nofollow">Quick Locale Switcher</a>
</li><li> <strong><a href="https://addons.mozilla.org/firefox/addon/locale-switcher" rel="nofollow">Locale Switcher</a></strong>
</li><li><a href="https://addons.mozilla.org/firefox/addon/language-manager" rel="nofollow">Language Manager</a>
</li><li> <a href="https://addons.mozilla.org/firefox/addon/simple-locale-switcherSimple" rel="nofollow">Locale Switcher</a>
</li></ul>
</li><li> Tenforums tutorial <a href="http://www.tenforums.com/tutorials/5440-user-account-add-windows-10-a.html" rel="nofollow">How to Add a New User Account in Windows 10</a>
</li><li> <a href="/en-US/kb/profile-manager-create-remove-switch-firefox-profiles" rel="nofollow">Profile Manager - Create, remove or switch Firefox profiles</a> (No need to try this if you just set up a Windows account they each have their own Firefox profile)
<ul><li> Explanation: <a href="/en-US/kb/profiles-where-firefox-stores-user-data" rel="nofollow">Profiles - Where Firefox stores your bookmarks, passwords and other user data</a>
</li></ul>
</li></ul>
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<p>Update: also see
<em>cor-el <a href="#answer-942963" rel="nofollow">said</a></em>
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<blockquote>
Note that you can also use a command line switch to start Firefox with a specific locale if you have multiple locales installed.
<ul><li><a href="https://developer.mozilla.org/Command_Line_Options" rel="nofollow">https://developer.mozilla.org/Command_Line_Options</a>
</li></ul>
You can create a desktop shortcut with the "-UILocale xx-xx" switch appended to the command line to start Firefox with a specific locale.
<ul><li>Start &gt; Run: firefox.exe -UILocale en-US
</li></ul>
</blockquote>John 99 thanks for your your comment.
I have the german firefox and language packs version installed2016-12-08T18:28:03-08:00gertrhttps://support.mozilla.org/en-US/questions/1147354#answer-942836<p>John 99 thanks for your your comment.
</p><pre>I have the german firefox and language packs version installed.
</pre>
<p>After numerous trials following <a href="https://support.mozilla.org/en-US/kb/use-firefox-interface-other-languages-language-pack" rel="nofollow">https://support.mozilla.org/en-US/kb/use-firefox-interface-other-languages-language-pack</a> it worked to change from en to de.
Why&nbsp;??? I don't know
</p>Hi gertr,
Firefox switches languages ok for me.
So a few questions to see if I can figure out what i2016-11-26T04:42:48-08:00John99https://support.mozilla.org/en-US/questions/1147354#answer-939112<p>Hi gertr,
Firefox switches languages ok for me.
So a few questions to see if I can figure out what is happening
</p>
<ul><li> Did this work previously has it just stopped working now&nbsp;?
</li><li> Do you have an English? German? or some other Firefox installed&nbsp;?
</li><li> Which language is the Firefox interface using at present&nbsp;?
</li><li> Have you got language packs installed (Which ones&nbsp;?) &amp; can you see them in about:addons languages tab&nbsp;?
<ul><li> See also <a href="/en-US/kb/use-firefox-another-language#w_how-to-manage-language-packs" rel="nofollow">Use Firefox in another language</a>_how-to-manage-language-packs
</li></ul>
</li></ul>