I migrate ojs 2.4.8 to 3.1, db : postgres.
In some publicacion I have two Language (spanish and english). When I change with the selector, part of gui not change spanish to english.
If you reload the page in your browser after switching to a new ui language, does the problem persist? This could be related to the browser partly caching some content. Also, you could check whether you have defined the menu items manually - in that case, they may not be translated if no translation was entered.
its happened to me too, and I found out that the menu item names have not been translated in my second lang,
go to the “navigation menu”->“Navigation Menu Items” and edit the items and check is their name has the value in both langs.