When it comes to local derbies, if you have here Barcelona vs Espanyol instead of Real; you should give in Mexico option Club Atlas instead of America.
With all do respect, the Espanyol and Barcelona derby is definitely a thing, but why wouldn't you put in the El Classico? Or maybe put 2 answers for teams like Barca and Arsenal where they have several derbies.
Great quiz! Although maybe add the option to have alternative spellings for Fenerbahce, as "Fenerbache" or "Fenerbace" because the spelling is hard :) Anyways, congrats on the great idea!
Krakow, Belgrade and Athens are massive ones. West Ham - Millwall is probably the most famous English one, but I'd give the South Coast Derby (Southampton - Portsmouth) a mention. It hasn't been a common fixture lately, but I can guarantee it's been absolutely crazy when it has happened. Some fierce Italian ones (albeit lesser known due to lower status of the teams involved) are Pisa - Livorno and Palermo - Catania
Joining the South Coast Derby, other local derbies that tend to start before noon (to minimise pre-game drinking), yet still end up having arrests, include West Brom-Wolves and Luton-Watford.
The quiz captures good variety across the globe, and while everyone can demand to have their favorite locales added, doing that would make the quiz less appealing to a broader audience. So just add St Pauli vs Hamburg as well as Gladbach vs Cologne, and then we can be done with it. ;-)
Nice quiz, nominated. Could you add a few type ins for Fenerbahce? Probably the most obvious one that I was trying was Fenerbache. Agreed with the above that El Classico is not a derby, just a rivalry. Only other suggestion is for Arsenal could Chelsea also be added as a type in - on that basis probably the other 11 London EFL teams too, but whilst the North London Derby is a big and famous one, so is AFC vs Chelsea. Thinking is there any French ones, only one I can think of that's really local and obvious is Lille vs Lens.
A non-local derbies version would be cool, or a part 2.