Mexico is the biggest Hispanophone country, as well as the one which has the most contact with the United States, so if schools in the US have to pick any dialect to teach, it should be Mexican Spanish. (IIRC Spain is the third largest Hispanophone country after Mexico and Colombia).
Yeah, but castellano happens to be a name for the language, not for the Castillian dialects. Mexican Spanish is a dialect of castellano (actually, a group thereof, as there is variation within Mexico too).
“English” is the word for the language I’m speaking now, but I certainly don’t think the dialect spoken in, well, England is more normative than American or Australian English. Neither is the dialect of “Portuguese” spoken in Portugal necessarily better or more normative than the Brazilian variety.
I would love to see like a YouTube video of different Spanish speakers from different countries all saying the same thing (like a passage from the Bible or Cervantes or what have you), so I could see if I could suss out the accents. Same with Paris French vs. Montreal French.
I’ve mentioned this on the SDMB before but it bears repeating. Decades ago, we were on a bus tour of Europe, and there were a handful of Canadians in the group. At least two of them were Quebecois women who spoke both English and French (of the Canadian variety). I had some difficulties at a restaurant in France and asked our Canadian friend to help out: she refused. She said that she wouldn’t understand a word the Parisian said, nor the Parisian her.
I didn’t buy it (and still don’t). I can pick up about 99% of what they’re saying on British TV shows, and I’m sure yer average Brit could understand me perfectly (allowing for regionalisms and colloquialisms and what have you). I see no reason why Paris-Montreal French couldn’t be mutually intelligible.
OK, and neither do I think that the Spanish from wherever is more correct than that of wherever else except when we get to the realm of pidgins, but what’s that got to do with castellano being one of the names the Spanish language receives in Spanish?
Three accent/language stories:
There are many languages I recognize spoken despite not knowing a single word to speak. That’s not exactly the same as recognizing dialects, but if a language is a dialect with an army and a navy, surely it is similar. For example, I can usually hear the difference between Russian and Ukrainian.
I was recently in Japan. I was introduced to a young woman who had recently spent a year abroad in the US. When i spoke, her jaw dropped, and she said, “that’s not the accent i expected”. She had been in Alabama, and I’m from the Northeast.
My anglophone mother used to be fluent in both German and French, but she learned French first. People she spoke to in German said she spoke it with a French accent.
Yes, my only visit to Spain was to Barcelona recently; I had hoped for an opportunity to use what little Spanish I had left from high school many moons ago. I found that Catalan seemed to use slightly different words, some words that were variants on French or Italian words, some odd-sounding tenses… kind of like that dream where you can almost understand what people are saying. At least a lot of the signs were in both Catalan and Spanish.
This is not what the OP is discussing because Mandarin and Cantonese are completely separate and it’s not a matter of accents. It would be the equivalent of being able to tell Italian and French apart.
As only Hong Kong in that list speak Cantonese, it wouldn’t take that much exposure to be able to tell the others from there.
Somebody earlier mentioned Germans learning to speak British English and choosing to speak American English. I just came across this interesting video on YouTube:
Why Do GERMANS speak AMERICAN ENGLISH?
The girl in the video definitely does NOT sound “American” to me. Here’s the comment I posted:
Rather than reply to other comments, I’ll give my own perception here, as an American (Washington state, the northwest corner of the continental U.S.).
First, I will confirm that your “American English” pronunciations are correct and accurate, and your grammar is excellent.
Do you sound “American”? No. But where other commenters are saying “German accent”, I say “German rhythm”. What do I mean by that? I mean that every language (and every different country where a particular language is spoken) has its own meter, its own melody, its own “flow”. I sometimes have difficulty following the dialogue in British movies and television shows. The difficulty does not come from the actors’ pronunciation or “accent”. The difficulty comes from the fact that the British speak English with a different rhythm, different melody, different “flow” than what I am accustomed to. If I’m watching a British television show, after one or two episodes I become accustomed to their “flow”, and from then on I have no trouble.
When you were speaking individual, isolated words toward the end of the video (when you were comparing American and British pronunciations of the same words), they sounded perfectly “normal” to my ears. But when you string the English words together into sentences, while your pronunciation and grammar are excellent (and perfectly understandable), your “rhythm” is German, not American. I would need to listen to much more of you before I could give a detailed explanation, but here is the main thing that I noticed:
You “clip” words (cut them off short). As an American, conversing with fellow Americans, or watching American movies or television, I’m accustomed to hearing words flow smoothly from one word to the next. Basically, I hear my language in full sentences, not individual words.To a small extent, to my ears, I hear you “speaking a sequence of words that make sense”, rather than “speaking a sentence”. When I hear a fellow American speak, the last part of one word slides right into the beginning of the next word. When you speak, I hear a distinct break between each word. It’s quick and it’s subtle, but it’s there.
Please take my thoughts as “constructive criticism”. Your English is perfect, but it doesn’t sound “American”. In all honesty, you don’t need to “sound American”. You speak English more than well enough to blend in with Americans. Only an idiot American would complain; most would be happy to meet a German who speaks English as well as you do 
Well, my OP was regarding the former, and it would come up in the scenario I described in the OP - watching a TV show or movie where someone was speaking English, and later hearing people saying “that actor has the wrong accent” - for example, watching a movie about an upper-class English spy but the actor is American and speaks the character’s lines in a strong California accent.
The latter aspect is interesting though, so it’s been good to hear people’s personal experiences of that too.