Firefox Community Forum

Fix for RangeError: invalid language tag and client-side exceptions in Firefox on Linux

Hi everyone, I was experiencing persistent JavaScript errors in Firefox on Linux when loading certain modern websites (e.g., built with React or Next.js). The browser console showed messages like:

   RangeError: invalid language tag: "chrome://global/locale/intl.properties"

   A client-side exception has occurred (see the browser console for more information)
   React error #418 with minified stack traces

This happened even in Safe Mode, with all extensions disabled, cookies/cache cleared, and Enhanced Tracking Protection off. ✅ Root cause and fix:

Turns out the issue was related to missing or broken locale configuration in Firefox. To fix it:

   Open about:config

   Create a new string entry:

       Name: intl.locale.requested

       Value: en-US (or fr, en-GB, etc. — any valid locale)

   Restart Firefox

After adding this key, all affected pages started working correctly. The invalid "chrome://global/locale/intl.properties" error in intl.accept_languages disappeared as well — it seems that was just a side effect of the missing locale setting. 🔁 Summary:

If you’re seeing RangeError: invalid language tag and React crashes, try adding intl.locale.requested manually. This fixed the issue entirely for me on Linux.

Hope this helps others!

Please,

I have a Debian 11 VAIO laptop, with Firefox ESR 115.14.0esr 64.

I have tried the settings menus (there is nothing about translation there, not even in languages.

Tried as well the about:config (several entries).

Nothing happens, annoying auto-translation bar shows up all the time and automatically translates several languages.

Really can't stand any longer...

Please help!

Appreciate.

I have downloaded and installed the Japanese language pack. I switched to Japanese in the settings, but English words still come out. (in fact, I'm on Japan settings typing this) According to others, I've done it correctly, but no luck for me. I saw a setting that said it isn't supported on the American browser. If that's the case, I need a better browser. It works fine on my phone, which is why I am so perplexed with this. If you could offer some advice I'd appreciate it. Thanks for your time

Lately, one particular page keeps opening in Chinese instead of English. I've checked with friends and coworkers, and it loads in English for them without any issues. I've already gone through my language settings to make sure everything is set to English, and I don't use any VPNs while browsing. Any suggestions would be greatly appreciated.

Hello,

Recently noticed how browser changes the language on restart from English (default language ) to Russian. The affected websites swapped interfaces to Russian language.

Is it part of some kind of A/B testing, locally distributed malware / spyware or just simply embedded ML ops?

I am using macOS.

Thank you, Kind regards, Dmitrii.

Hi, I am curious to know why I can't completely remove the Dutch language in the language settings. When I installed the browser it was automatically set-up to Dutch - a language don't speak - then I was able to add English but some functions like spelling corrections are still in Dutch. I would like to get rid of it. I have the same problem with German on another computer. Thanks!

Firefox 139.0.1 on W11

When I open a page in a foreign language, such as English in my case, I don’t have access to a translation module. Yet this feature exists in Firefox, but I don’t understand why the translation isn’t being offered.

When I search for "Translation" in the Settings, I do find this translation module. I’ve downloaded all the languages and restarted my browser.

When I click on the Settings button for this module (see screenshot), in the section “Translations will be done automatically for the following languages,” I can't add any language there.

Despite this, when I go back to a web page in a foreign language, like a news article in English, I still don’t see the translation icon in the address bar.

Can you help me resolve this issue? Can I provide any additional information to help?

Thank you

When I set Firefox's language to English, the translation panel doesn't automatically appear or ask to translate other languages when I'm on English websites. I would like to request a feature that allows the translation panel to always be pinned to the search bar. Even better, if possible, it could also be pinned to the right-click context menu.