I use GSX most of the time these days, but I do miss from AES the fact that it greets you in Spanish, French, or Italian when landing in airports in those countries. Does anyone cleverer than me know how the AES voices know which voice set to trigger? Does it read the airport AFCAD file somehow?

I would presume by reading the ICAO code of the airport. In most cases, you only need the first two letters to get the country (and in some cases just one).