What is your location? Sometimes if you are outside an English area is can cause language problems.

Try reinstalling the English version from Download Firefox For All languages And Systems {web link}

I'm in Canada and I connect to the internet with a VPN through the US. The problem happens with or without using the VPN.

I tried reinstalling but it hasn't made any difference

If you visit a site that tells you about your IP address, does it match the U.S., or Germany, or something else?

For example:

https://www.iplocation.net/

You also could check your language preference. This is set on the Options page:

• Windows: "3-bar" menu button (or Tools menu) > Options
• Mac: "3-bar" menu button (or Firefox menu) > Preferences
• Linux: "3-bar" menu button (or Edit menu) > Preferences
• Any system: type or paste about:preferences into the address bar and press Enter/Return to load it

Scroll down to Language and Appearance, and in the Language section, click the Choose button. Make sure Firefox lists your languages in the order you prefer. (Example screenshot attached.)

My son changed the VPN to a server in Germany. Now that I've switched back to an American server everything's fine.

Thanks for your help.

That was very good work. Well done. Please flag your last post as Solved Problem so others will know.