I have a buddy who learned English as a second language early in life and he has a fluent Irish accent. I've never been able to wrap my head around that one.
I lived in South Korea for a while and I met a South Korean young lady who had learned English from an Australian teacher. This Korean girl had the most beautiful Australian accent with a hint of Korean. She was very talkative, Asian people get excited when they meet english-speakers so they can practice speaking English with us. So she talked a lot. It was a beautiful culture medley.
As an American I feel like either US or UK could be considered the "normal" one, UK or AUS the "fancy" one, and US and AUS the "wildcard" (from the UK perspective).
No no, I speak a combination of the three. Although American English dominates my accent. That's what you get when you grow up watching English-speaking media. You pick up their accents and you make one of your own.
I got mine originally from TV, as in my country everything is subtitled, so that means I ended up with an americanized accent (it isn't really an "american" accent because there is no such things as an american accents but rather several).
It was of course poluted by my own native language (portuguese, from Lisbon) accent.
Then I went and lived in The Netherlands for almost a decade so my accent started adding dutch "effects" (like a "yes" that sounds more like "ya", similar to the dutch "ja").
And after that I lived for over a decade in England, so my accent moved a lot towards the English RP accent. In fact I can either do my lazy accent (which is the mix of accents I have) or pull it towards a pretty decent English RP accent if needed for clarity.
By this point I can actually do several English Language accents, though mostly only enough to deceive foreigners rather than locals - so, say, a Scottish accent that will deceive Americans but Brits can spot it as not really being any of the various Scottish accents - including the accents of foreign language speakers in English (i.e. how a french or italian will sounds speaking english or even the full-force portuguese accent when speaking english, which I don't naturally have anymore).
That said, IMHO it is very hard for somebody who grew up in a foreign country speaking a foreign language to fine tune their accent so that it sounds perfect to the ears of a local, and this is valid for all languages, not just English.
It's just as bad in spanish. I'm an american with a colombian paisa accent in spanish and it messes with the mexicans. They love it since it's not what they usually hear.
I once did one of those quizzes that figures out where your American accent is from and I got mostly LA and midwest. Makes sense since I learned from watching TV shows.
I have read British and American books galore (i.e. thousands), and I've listened to English (BBC, BFBS) and American (AFN, Movies) audio sources. My vocabulary and accent is a wild mix of both, so the British consider me American, and the American think I'm British.
How about Northside Dubliners picking a Dub Southside accent to sound posher, or Southsiders picking a Northside Dub accent to sound more gangsta? It's an actual thing. ^^
I've done so many accents at this point I don't even know what my real accent is anymore, but people always think I'm actually from New York or New Jersey until I start talking.