You can tag/label numbers with various country names as needed. Scroll all the way to the bottom and choose Custom.
Or if you need to see which number someone is using, just scroll to the top of the messages window on the conversation of said friend with many numbers (where it has call, facetime, contact buttons)
Then tap Contact and the window will slide over to show you said information. The number currently being used will be highlighted in blue.
It's the same thing for calls, Goto recents > find said friend > tap the blue arrow > and the number used will be in highlighted in blue.