How to change the interface language in Mozilla Firefox

If you are not a native English speaker, you might want to use apps in your language. That includes any software, starting from your operating system to your favorite Office productivity suite and your primary web browser. If your browser of choice is Mozilla Firefox and you do not know how to change its user interface language, then you should read this guide. We show you two ways to get Firefox working in any language that you want:

NOTE: We assume that you already have Mozilla Firefox installed but it is not in the language that you want.

1. Download Mozilla Firefox in your language

The first and probably the easiest method to use Mozilla Firefox is to download it directly in your language and install it on top of the existing Firefox installation. To do that, visit this official Firefox website: Download Firefox in your language. It looks like this:

On this website, you can download Firefox in any of the 90 languages that it supports. To do so, enter the name of the language you want in the "Search languages" field, or scroll until you find it in the list beneath it.

After you find the language that you want, look on its right side. There, you have a series of links for Firefox, all in that language, but for different operating systems. Click or tap on the one that matches your operating system and its version (64-bit or 32-bit), and the download starts. For example, we want Firefox to use Romanian as display language, and we are using Windows 10 64-bit, so we have to download the Romanian Windows 64-bit version of Firefox.

NOTE: If you do not know what version of Windows you have, this guide can help you figure it out: What version of Windows do I have installed?.

Once you download the Firefox installer file, run it and follow the steps of the install wizard. In the end, you should have a fully functional Firefox that displays its user interface in the language that you chose.

2. Download a language pack for Mozilla Firefox's user interface and enable it in its settings

Another method that works just as well and which some people might prefer is to download, install and enable a language pack for their Mozilla Firefox browser. Open Firefox and visit this website: Firefox Add-ons - Dictionaries and Language Packs. It looks like this:

On it, there is a long list with all the languages in which Firefox's interface can be used. Scroll down until you find the one you want, and then click or tap the Language Pack link to its right.

The previous action takes you to that language pack's webpage. On it, click or tap the "+ Add to Firefox" button.

Firefox now asks if you want to add that language pack (add-on) to Firefox. Click or tap Add to continue.

After the language pack has been added to your Firefox, click or tap on OK to close the dialog.

Now, all it remains for us to do is to enable the new language and make Firefox use it for its user interface.

To do so, open a new tab and type about:config in its address bar. Then press Enter on your keyboard.

Firefox might show a warning that "This might void your warranty!" because you are about to change advanced settings. This warning may not be in English, but in a different language, depending on what you have installed on your PC. Click or tap "I accept the risk!" or the only blue button that you see.

Firefox shows you a long list with advanced settings that you can change. It looks like this:

In the Search field at the top, type intl.locale.requested or copy and paste this text. This filters the list of settings and should show only one setting, named intl.locale.requested. Double-click or double-tap on it and Firefox opens a small window in which the current display language code is shown. For example, if Firefox is now using US English, you should see en-us.

Delete the current language code and, in its place, type the code of the language pack that you want to switch to. Then, click or tap on OK. For example, we want Firefox to use Romanian as a display language, and its code is ro. So, we have to type ro and press OK.

If you do not know the code for the language pack that you have installed and wanted to activate, you can find the list of all the language codes here: Mozilla Web Localization Dashboard.

Once you entered the language code and pressed OK, all that remains for you to do is close Firefox completely (all its windows) and restart it. When you restart it, Firefox is using the new display language.

What to do if you do not find the "intl.locale.requested" setting in the "about:config" tab

There are situations that we also stumbled upon, in which Firefox does not show you anything when you are searching for the intl.locale.requested setting in the about:config tab. We know for sure that this happens in the last version of Firefox that we used: Firefox 61 (64-bit).

However, that does not mean that you cannot use this method to change the display language. There is, however, an additional step that you must perform, and that is to create the intl.locale.requested setting yourself. In the about:config tab, right-click anywhere in the list of settings (or on any setting), and you should see a small contextual menu. In it, click or tap on New and then String. If Firefox is in a language that you do not understand, click the only option with an arrow on its right (it is the fifth when going from top to bottom), and then in the submenu that opens, choose the first value from the top. This is always the equivalent of choosing New and then String.

In the "New string value" window, type intl.locale.requested, and then press OK.

Firefox then asks you to "Enter string value." Type the language code for the language pack that you installed previously and which you want Firefox to use to display the user interface.

Click or tap OK and restart Firefox. Then, your favorite web browser displays its user interface in the new language that you installed and enabled.

Did you switch the interface language for Mozilla Firefox?

These are the two ways that we know for changing the language used by Firefox to display its user interface. Do you know others too? Did you find it easy to change Firefox's display language? Share your thoughts, opinions or questions, in the comments section below.