I think that Czech and Slovak languages are incredibly similar to each other. often times, when reading the instructions on some product in both languages, they differ by one word here and there. I would be willing to guess that no speaker of these languages would be able to differentiate one from the other.
A cool variant on this game could be "guess where this English accent is from."
("I would be willing to guess that no speaker of these languages would be able to differentiate one from the other" – I highly doubt that. Dialects/languages differ more and more the closer they are to your own; I can tell if someone grew up a 15 minute drive away from me, but if the choice is between a place that is e.g. >3 hrs north vs >4hrs north I have a really hard time placing them.)
A cool variant on this game could be "guess where this English accent is from."