Adding a country selector

Hi all,

I’m not sure this is strictly a WordPress question, but I don’t know where else I would ask this

I’m trying to add a little drop down menu that contains a number of flags. When a flag is selected, the phone number at the top of the site will change to reflect this, and will show my number in the appropriate country

I have no idea where to even start with this. I don’t want to create an entirely different subdomain as the only thing that will change is the number, but I also want the number to change on every page the user visits.

Is this possible?

I have no code to show as I have no jumping off point, but I would be very grateful for any help