Highlight discrepancies

Hello everyone. I have a list for which column A is the room number and column B is language. I wish to highlight the discrepancies of languages within the same room number. Could you indicate me an automatic way to do this?

512 english
512 english
513 french
513 spanish
514 french
514 french
515 spanish
515 spanish

In the sample above, I would like to highlight the room number 513.

Hi and welcome.

You could use "Conditional Formatting" with a formula like this:
=COUNTIFS($A:$A,$A2,$B:$B,$B2)<>COUNTIF($A:$A,$A2)

See attached.

BSB

That's perfect. Thank you so much.

No problem. Happy to help

BSB