Language priority when a page is displayed

Issue

• Which localization is being used when a page is displayed?

Environment

• Liferay Portal DXP 7.0+

Resolution

• The language of a page can be determined by 3 factors:
  • the page URL (whether there is a language id)
  • GUEST_LANGUAGE_ID cookie
  • jsessionid cookie (session variables)
• If we are using the default portal property:prepend.friendly.url.style=3, then we can ignore the page URL factor.
  
  
• Language settings are being stored in one cookie in your browser, which is GUEST_LANGUAGE_ID. 
  
  
• The way it works is the following: 
  1. if set for user, read that
  2. if not set for user, read group (site)
  3. if not set for site, read company (portal)
     
     
• The result will be one cookie: GUEST_LANGUAGE_ID. If the guest user sets the language to another then the default, it gets saved to the GUEST_LANGUAGE_ID. 
• GUEST_LANGUAGE_ID is being used by both the Guest user and a logged-in user. If the user logs in, then its language ID will be fetched from the database and gets put into the same cookie. This will overwrite the guest's language preference, which will be lost.
  
  
• As for the jsessionid, it gets reset whenever a user logs in and logs out. This means that the previous guest user's languageId would also not be retained by the session.

Additional Information

• The following articles could be helpful as well:
  
  • What Language is Set for Liferay's Web Pages?
  • How the cookies are being used in Liferay portal
  • Incorrect Language Locale Appended to URLs for Authenticated Users