Issue with multi tabs with user preference

Is there any way to determine how many instances of browsers are open and to update the user preference in every open tabs?

I was just checking for a solution to a problem where suppose a user has opened multiple tabs. and he's updating user preferences in one of the tab, then the same preference should be available to all open tabs.

Please see that the word "user preference" is actually application specific.

For example, suppose if a user has opened two tabs, and then in one of the tab he selects the language as English from French, then if he is clicking on any action on different tab, he should be given the language as English only.

Since we can not clear browser cache, there must be some way to get this done.