I don't have much to add, except that in order to pull it off, you have to have a very good ear for dialect, and the ability to not let the dialect get in the way of the story. Otherwise, you can come perilously close to the dialogue sabotaging the story. I'll let a master add his two cents: in the "author's note" that precedes The Adventures of Huckleberry Finn, Mark Twain wrote: "In this book a number of dialects are used, to wit: the Missouri negro dialect; the extremest form of the backwoods Southwestern dialect; the ordinary "Pike County" dialect; and four modified varieties of this last. The shadings have not been done in a haphazard fashion, or by guesswork; but painstakingly, and with the trustworthy guidance and support of personal familiarity with these several forms of speech. I make this explanation for the reason that without it many readers would suppose that all these characters were trying to talk alike and not succeeding."
Words are important; if you want to convey a Scottish accent, for example, have your character say things like "aye, cheers lad" (maybe that's too stereotypical?) But basically, for British accents at least, you should pepper their dialogue with British slang, and whenever there's a word they would spell differently (gray vs grey or mom vs mum) then spell it that way. For a French accent, use the word ah a lot ("Ah, Monsieur Barron, this wine is excellent!") and pepper French words throughout their dialogue. If they're not the type to mix French with their English, then lean heavily on loan words. Imagine the character is extremely proud of the fact that English has so many French expressions that he takes every opportunity to use them. This character's every sentence would employ at least one item from this list https://en.wikipedia.org/wiki/List_of_French_expressions_in_English such as faux or coupe de grace. That would be a subtle way to convey French origin. Or you could simply write it phonetically. French isn't one of those accents where it would be unintelligible if it was spelled "thickly" as far as I've read.
In novels written before global communication and travel were more convenient, you might have a person who hadn't traveled more than a few miles from home. Consequently, a person in England might not know what a German-English accent sounds like. Thus, writers would include the accent in their dialog, substituting 'v' for 'w,' for example ("where" becomes "vhere"). As global communication and travel became easier, and especially with the advent of sound movies and the Internet, accents became more familiar to people. Over time, people became accustomed to stereotypical accents associated with various locations. If I say "Russian accent," you probably have some idea of what that sounds like. The same goes for Australia, England, Germany, India, China, and so on. So writing an accent in dialog becomes redundant, and slows down what the reader is already thinking in their head. It might be necessary to pepper the dialog with reminders (if you have four nationalities, those little reminders can help keep the characters straight in the reader's mind). But writing the dialog completely in an accent interrupts the flow of a story, and turns into bad writing. There's an art to how to employ accents in dialog, and part of it is subjective. I personally couldn't stand Hagrid or Fleur in Harry Potter because of their accents. Their dialog was a chore to read. Others don't mind it as much. The best advice I can give is to read a great deal, and write it like you want. You can always adjust it in editing, and get an idea of where your comfort zone is. Not everyone will like the way you go about it, and that's okay. If you write the full accent all the time, I probably won't read it, but if that's what makes you happy, go for it.
This depends very much on the POV, in my opinion. If you're using a limited POV, as most people do, then spellings should correlate with the POV character. An American character hearing a Brit speak is going to hear "color", not "colour." Noo! That's a cartoon Frenchman, not a real Frenchman.
Chiming in to also disagree. Mom and Mum are actually different words, so you could make that swap. But grey is gray. The spelling is determined by the spelling standard of the narrative, and won't change with the speaker.
There's a chapter in ELT textbooks that unravels misconceptions & stereotypes re common traits of other nationalities speaking English, so it's worth seeking out. A tEFL teacher might help me here? The only example I remember is our use of 'phrasal verbs,' but, you see, the French language has no phrasal verbs, so monsieur appears terse or stand-offish in his usage of English, if somebody could back me up, [i.e] I'm struggling, umm si vous soutenez-moi, peut-etre? [Yes, he says 'support me, please,' which presents an air of pomposity which is not intentional...example] There's a page for Spanish, Russians & a chapter on the shouten word dialect of the United States, of course.
I've never seen spelling changes based on the speaker (at least, not that I've noticed, and I'm pretty sure I would've). It's actually fairly awkward for me to read an American character who spells words in a British way, or who uses British colloquialisms (i.e., "lift" for "elevator"). Because I'm an American, I notice that more than if an American writer flubs writing a British character. Of course, that's just two nationalities. Alan Glynn (The Dark Fields, aka Limitless) screwed the pooch by using definite European colloquialisms (i.e., "lift" for "elevator") with a character from New York City. A lift and an elevator are two different words to describe the same thing, but putting European jargon in the dialog or narrative of a New York character blows holes through the emotional impact of a lot of scenes. It's like seeing a boom mic or a cameraman's reflection in a horror movie; you're suddenly very aware you're not actually in the story they're attempting to tell. It's kind of a tangential point to the issue of accents, but if you're going to have a character from a place, they should come across as a native. Glynn also used some British spellings (i.e., colour) that showed me I wasn't reading a story with an American character. He almost had it, but occasionally tripped up. Oddly, if he'd just had the character be a British expatriate living in New York, I'd have been okay with that. As it was, the pooch done got screwed.
Just on a technical note, that's not a colloquialism. The thing that Americans call an elevator is called a lift in British English. It's not a colloquial term for the more formal 'elevator'--we just don't use the word 'elevator' at all.
But that means something different. We're talking about the thing inside a building which Americans call an elevator and Brits call a lift. And the British word "lift" is not a colloquial term for the more formal "elevator". The word "lift" is used in both formal and informal contexts.
We just don't use the word QWEEBLECUMFYNESS (I deliberately didn't use a foreign word because English has so many loan words that I'd struggle to pick one that doesn't fall into that category) at all. We do use the word elevator - even if we use it to mean something different to what the Americans mean...although they also use it to mean what we mean when we use it.
Ok, I thought it was obvious from the context that when I said we don't use it, I meant that we don't use it to mean the thing in a building that carries you vertically from one floor to another.
All I'll say on this is that I couldn't get beyond the first two pages of Irvin Welsh's Trainspotting.
I gave up on it too. I did find I started to tune in after a while and the written-in accent became slightly less annoying. But nonetheless, it was a constant distraction.
So I just looked up "colloquialism," and I've been using it wrong for twenty some-odd fucking years. Awesome. I'm going back to bed or to the liquor store. One of the two.
This! For an example of what not to do, check out Gelsey Kirkland's 1986 autobiography Dancing on My Grave. The writing of the accents is so bad, my paperback copy has a disclaimer stating that it isn't intended to offend. As an example of why it's bad, Kirkland makes Mikhail Baryshnikov sound unintelligent (the man is extremely intelligent and well-read). Also, in Kirkland's version of his accent, his English somehow never improves--despite having lived in the U.S. for eight years at that time, having American coworkers and American live-in girlfriends, and his taking part in documentary films that show that it improved. My MC, Alexei, is Russian, and I don't claim to write him perfectly, or even well. But I do write him respectfully. The reader knows Alexei has an accent without my spelling out his pronunciation because he's introduced this way: "I'm maybe a bit early, I think." He had a Russian accent. Elsewhere in the story, Alexei swears in Russian. In another place in the story, he is awakened from a deep sleep at three A.M. and knows his syntax is off but is too tired to remember the proper way to say it in English. The one exception to my "no spelling phonetically" rule is when Alexei calls the other MC, Katherine, by her name (he usually calls her by a nickname). It's implicitly stated that Katherine loves the way he says it, so I feel it's done respectfully: She even loved the way he said her name: "Kas-ren." His accent made consonants sound soft and sexy. Here's my approach to writing Alexei's accent: Respect the character, always. Ask yourself (or ask your character): 1. How long has this character lived in the U.S. (or whichever English speaking country)? Has he moved around a lot? Where has he lived, and for how long? 2. What was his social class in his former country? 3. With what social class does he most often work and socialize now? What does he do for work? 4. Very important: How did he learn English? (Someone who learned English from watching old movies speaks differently than someone who took a Berlitz course, and someone who learned from watching television news speaks differently from either of them. Each would use different slang and use different levels of formality / contractions._ 5. At what time of day or under what circumstances is his English best, and worst? How does his English sound when he's stressed out, tired, or angry? Watch lots of YouTube videos (not movies) / listen to podcasts of a person with an accent closest to the character's accent after answering the questions above, and write accordingly. If possible, chose one person as your inspiration so you get the "music" of their accent: the rhythm of their speech, speech patterns such as whether or not they use contractions (and if so when), which words they consistently use out of order, unusual syntax, phrases they use a lot, etc. . For my MC, Alexei, when I go back to polish his dialogue I watch YouTube clips of my "Inspiration Person" while I'm working, and I compare their speech rhythms. It was during this process that I noticed my Inspiration Person inserts the word "maybe" in specific places in his sentences (see above). If your character is French, there are tons of old cooking videos hosted by French people from various backgrounds. Cooking shows are excellent because there's so much ad-libbing in their own words. Jacques Pepin is from Lyon but worked in Paris. If you choose one with his friend Jean-Claude cooking with him, J-C has a different French accent. The late Pierre Franey had another. Madeline Kamman, still another. I hope this very long post helps someone! Good luck! (edited to remove a repeated sentence)
It's the main reason I couldn't get past a few pages of Requiem for a Dream. Shame, because it's one of my favourite films!