Migrate sites with multiple languages from 6.1.1 to 6.2.2 CE GA3
Set locale.prepend.friendly.url.style=0 in portal-ext-default.properties.
Set control panel default language to en.
Create site page for site that is not default language site.
Navigate to newly created page.
Navigate to site landing page that is default language.
Return to previous page by browsers back or by typing in url.
Cookie is now that of default language and url might get prepended with default or previous site language. This does not happen 100% of the time for some reason. UPDATE: Reason is that firendlyurl is not always saved correctly into the database.
Go edit a site-page of a site that is not portal default language site. For example if your default site is EN edit a secondary site that has a different default language and is not the default site.
Site administration -> Site Pages
Update any field except the Friendly URL -field, for example SEO -> Description and Save
The Friendly URL -field data will change to contain a numeric ID of sorts, possibly the layout ID.
But if you manually change the Friendly URL -field after migration you cannot reporoduce this effect anymore.
My guess is that during the save process liferay tries to check the friendly url but the check process gets the url prepended and it changes the friendly url to contain the pages id instead of it's original value.
In the example I appended the name field with the word TEST and pressed save.