Đổi ngôn ngữ trong trình duyệt firefox

  1.  Install the language pack for the desired languages.
  2. Type about:config into the address bar and press Enter.
  3. To bypass the warning, press the big button labeled "I'll be careful, I promise!".
  4. In the search box, paste intl.locale.matchOS
  5. In the search results, if intl.locale.matchOS is set to true, double-click it to set its value to false.
  6. In the search box, paste general.useragent.locale
  7. In the search results, double-click general.useragent.locale and set its value to the desired language.
  8. Restart Firefox for the change to take effect.
If you need to switch languages frequently, you may want to get an add-on like Simple Locale Switcher.