Disable geolocation in Safari
Your browser sends its list of preferred languages to websites. With other browsers, this is usually customizable, but not in Safari for macOS. On the Mac, Safari only sends the systemwide preferred languages.

To change it:  → System Preferences → Language &amp; Region.
Beware that doing this will change the locale used by your operating system.

On the other hand, in iOS 10 the systemwide language is set separately from the app-and-website preferred languages. Both can be found under Settings → General → Language &amp; Region.