[throw_a_grenade]

Non-joke answer for Europe is at least Latin, Greek or Cyrillic (български is already one of the official EU languages!). No reason to treat them differently, just don't allow for mixing them so you won't get homoglyphs. EURid (.eu-NIC) gets it mostly right I believe.

[account42]

The non-theoretical answer for Europe is just Latin because the names need to eventually be read by people who don't know Greek or Cyrillic.