Vocabulary notes on Acts 2:5-6; What is a dialect?

In Acts 2:6 we have the phrase

ἤκουον εἷς ἕκαστος τῇ ἰδίᾳ διαλέκτῳ λαλούντων αὐτῶν

they were hearing one each the own language being spoken of them

each one of them heard their own language being spoken 

The Greek ἡ διάλεκτος (note the feminine) is related to the English 'dialect'.  What exactly does it mean?

In English, a 'dialect' is commonly understood to be a sub-type of some language, but American linguistics professor John McWhorter says:

"The difference between a language and a dialect is mostly meaningless and entirely political."

Do my own slight oddities in English pronunciation and word choice - relics of a Minnesota childhood - constitute a dialect?  Probably not.  What about Norwegian and Swedish?  Some consider them dialects of 'modern Norse', but I'm not sure what Norwegians and Swedes think about that.

And what about Greek?  Most of the English translations of the phrase τῇ ἰδίᾳ διαλέκτῳ use 'in his own language', but some use 'tongue', and a few 'dialect'.  

Without native speakers of koine at hand, it's difficult to know exactly how the phrase would have been understood.  I refer the reader to some of the commentary on this verse, here.

Note that ἡ διάλεκτος is related to the koine verb διαλέγομαι, which is translated in a variety of ways, including 'I converse, discuss, reason, ponder' and so on.  Διαλέγομαι itself is a compound verb, with the preposition διά and the root verb λέγω.