I speak a bit of Spain Spanish, but with an Andalusian / Canary Island accent and grammar. The biggest problem you’ll probably find is that exactly the same word can have different meanings in different parts of the world.
I also speak some French, poorly. No idea with what accent.
I personally would not hesitate to recommend the Michel Thomas language courses. I learned more in twelve hours then I did in three years at school.
I root for the iggles, phils, flyers, and sixers. I eat beggles with cream cheese, and in the summer I'll get some wooder ice. I go fishing in the crick. If I fall in I'll dry myself off with a tal, and maybe I'll hang it on the ratty-ator to dry afterwards. I'll warsh the mud off my boots at the spicket outside. On vacation I'll go down the shore. If I need cash I'll tap mac, perhaps so I can order a cheesesteak (wiz wit) or hoagie. Maybe I'll see if my friends want to join me, and I'll ask them "jeet? And they'll answer "no, jew?" And at the end of the night, after a few citywides, I'll tell them "I'll see youse guys later"
You can also replace most of those nouns with "jawn"
I know European Portuguese and Canadian French, but I'm not good at either.
Edit: I just remembered this youtube channel called Wikitongues. You can hear people speaking in all kinds of different languages and dialects. It's fascinating. I found a dialect of French that sounds like Portuguese and French combined.
My English is an odd mix, and I've noticed that I tend to subconsciously emulate the accent of whomever I'm speaking with. Lately it's been mostly Texans, but as I work in an international environment I've been all over the place.
Not that many years ago my combination of coworkers resulted in some weird interpretations: Brits thought I was American, Americans and kiwis thought I was Canadian, and Canadians thought I was British. They all noticed something was up with my accent, but nobody was able to place it.
Same thing happens to me where I'll start emulating local accents. The result is no one can accurately guess where I'm from, even people from my own country. The general answer is "northern Europe" but not from the country of whomever is guessing. But it's the same reason… something is up with my accent, but no one is able to place it.
I speak a kind of wild mix of British English and American English. Like my pronunciation is probably closer to British but I'll also use some American terms, like "sidewalk" instead of "pavement". I guess it could be considered a variety of Euro English.
I speak standard (German) German, with a slight dialect of my region.
It depends on the reason I'm trying to learn the language. Neutral Spanish is a thing, it's usually well received in most latin american countries. If you learn something too region specific, usually doesn't.
I listened to a drunk Newfie (person from Newfoundland, Canada) give a speech once. I have no idea what he said. I heard they speak English there but I'm doubtful...
Neutral Spanish isn't a separate variant, so much as a separate register of the language, though. It's really just a thing I hear native speakers say when they don't realize that educated speakers from their country do, in fact, still have an accent, but it's more just down to vocabulary choice, rather than some major change elsewhere. Like, an educated Dominican isn't going to call a bus a guagua and they'll probably enunciate more clearly than they would in casual conversation, but they're not suddenly going to start using vosotros and distinción when they speak.
Whenever I hear a native speaker talking about Neutral Spanish, it's invariably followed by why I should try to speak like people from their home country, and that people from elsewhere don't really speak proper Spanish. It also tends to correlate pretty well with people telling me, "Yo hablo castellano, y por eso no puedo entender lo que dicen las personas plebes, ya que hablan español." for a nice dose of Latin American classism.
If you learn something too region specific, usually doesn’t.
My experience has been more that learners tend to not realize that certain things they pick up aren't universal, and/or that they're only acceptable in certain contexts, and then unwittingly pepper their speech with words and phrases from one country that are unknown/unacceptable in another, or use very informal/vulgar language in formal settings. Like, if I curse around my wife the way I would curse around my Mexican coworkers, she's scandalized by how vulgar the profanity is, and if I told my Mexican coworkers I had a fuinfuán in my backyard growing up, rather than a columpio, there's nearly 100% chance they're not going to have any idea what the hell I'm talking about.
It's more about the vocabulary and accent, not the level of education and correctness of the speaker. Usually neutral spanish is understood in all the spanish speaking countries of south america and spain, because, well, it's neutral.
A good example of neutral spanish usage in real life is dubbing. Most of our dubbing is done in Mexico, but the dubbing itself has no mexican specific words, mannerisms, or accent. Al dubbing is done this way, no matter the country, so only one version of the dubbing works for basically everyone.
As a matter of fact, there have been some experiments to challenge this, and use a more localized accent and vocabulary instead, and most went very wrong. The first Incredibles movie was dubbed with a argentinean flavor, español rioplatense. It was hated in Argentina, massive disaster, we pretend it didn't happen.
Also sometimes, when dubbing, we pick accents of different countries for different characters on purpose. Most of Grim Fandango was dubbed in Spain's Spanish, and some characters had Mexican and Argentinean accents, and that was relevant for the plot (Argentinean characters are shady people almost everytime). Think of the choice some media does to make someone speak English from England to make it sound more classy or something like that, basically almost every Spanish accent has its own stereotype.
It's weird, because neutral spanish is the language nobody speaks, because local accents and lingo, but everybody likes to hear because it's the most understandable.
I say, go for the most neutral vocabulary you can. You will have an accent anyway because it's not your native language.
Native English (US), learned the vaguely-Latino-Americano Spanish. That lasted until I went to Spain for a few months, now I have a strange amalgamation of Latino/Spanglish vocabulary with an Andaluz-ish accent.
You will speak the version that you learned. You will mostly notice regional differences in the idioms and synonyms of the words you know might be used more commonly in one region vs the other.
For example, in London you might hear people use boot instead of trunk.
But the majority of the words will be the same regardless of region.