List of English contractions from Wikipedia

english_contractions_dataset.json

{
    "ain't": "am not / is not / are not / has not / have not / did not",
    "amn't": "am not",
    "aren't": "are not",
    "can't": "cannot",
    "'cause": "because",
    "could've": "could have",
    "couldn't": "could not",
    "couldn't've": "could not have",
    "daren't": "dare not / dared not",
    "daresn't": "dare not",
    "dasn't": "dare not",
    "didn't": "did not",
    "doesn't": "does not",
    "don't": "do not / does not",
    "d'ye": "do you / did you",
    "e'er": "ever",
    "everybody's": "everybody is",
    "everyone's": "everyone is",
    "finna": "fixing to / going to",
    "g'day": "good day",
    "gimme": "give me",
    "giv'n": "given",
    "gonna": "going to",
    "gon't": "go not",
    "gotta": "got to",
    "hadn't": "had not",
    "hasn't": "has not",
    "haven't": "have not",
    "he'd": "he had / he would",
    "he'll": "he shall / he will",
    "he's": "he has / he is",
    "he've": "he have",
    "how'd": "how did / how would",
    "howdy": "how do you do / how do you fare",
    "how'll": "how will",
    "how're": "how are",
    "how's": "how has / how is / how does",
    "I'd": "I had / I would",
    "I'd've": "I would have",
    "I'll": "I shall / I will",
    "I'm": "I am",
    "I'm'a": "I am about to",
    "I'm'o": "I am going to",
    "innit": "is it not",
    "I've": "I have",
    "isn't": "is not",
    "it'd": "it would",
    "it'll": "it shall / it will",
    "it's": "it has / it is",
    "let's": "let us",
    "ma'am": "madam",
    "mayn't": "may not",
    "may've": "may have",
    "methinks": "me thinks",
    "mightn't": "might not",
    "might've": "might have",
    "mustn't": "must not",
    "mustn't've": "must not have",
    "must've": "must have",
    "needn't": "need not",
    "ne'er": "never",
    "o'clock": "of the clock",
    "o'er": "over",
    "ol'": "old",
    "oughtn't": "ought not",
    "'s": "is, has, does, or us",
    "shalln't": "shall not",
    "shan't": "shall not",
    "she'd": "she had / she would",
    "she'll": "she shall / she will",
    "she's": "she has / she is",
    "should've": "should have",
    "shouldn't": "should not",
    "shouldn't've": "should not have",
    "somebody's": "somebody has / somebody is",
    "someone's": "someone has / someone is",
    "something's": "something has / something is",
    "so're": "so are",
    "that'll": "that shall / that will",
    "that're": "that are",
    "that's": "that has / that is",
    "that'd": "that would / that had",
    "there'd": "there had / there would",
    "there'll": "there shall / there will",
    "there're": "there are",
    "there's": "there has / there is",
    "these're": "these are",
    "they'd": "they had / they would",
    "they'll": "they shall / they will",
    "they're": "they are / they were",
    "they've": "they have",
    "this's": "this has /",
    "those're": "those are",
    "'tis": "it is",
    "to've": "to have",
    "'twas": "it was",
    "wanna": "want to",
    "wasn't": "was not",
    "we'd": "we had / we would/ we did",
    "we'd've": "we would have",
    "we'll": "we will",
    "we're": "we are",
    "we've": "we have",
    "weren't": "were not",
    "what'd": "what did",
    "what'll": "what shall / what will/ what all",
    "what're": "what are/what were",
    "what's": "what has / what is / what does",
    "what've": "what have",
    "when's": "when has / when is",
    "where'd": "where did",
    "where're": "where are",
    "where's": "where has / where is / where does",
    "where've": "where have",
    "which'll": "which shall / which will",
    "which's": "which has / which is",
    "whilst": "while still",
    "who'd": "who would / who had / who did",
    "who'd've": "who would have",
    "who'll": "who shall / who will",
    "who're": "who are",
    "who's": "who has / who is / who does",
    "who've": "who have",
    "why'd": "why did",
    "why're": "why are",
    "why's": "why has / why is / why does",
    "won't": "will not",
    "would've": "would have",
    "wouldn't": "would not",
    "y'all": "you all",
    "y'all'd've": "you all would have",
    "y'all're": "you all are",
    "you'd": "you had / you would",
    "you'll": "you shall / you will",
    "you're": "you are/ you are",
    "you've": "you have",
    "noun's": "noun is",
    "noun're": "noun are"
  }

Run the code here in a JavaScript console of the Wikipedia page: https://en.wikipedia.org/wiki/Wikipedia:List_of_English_contractions

See https://gist.github.com/loretoparisi/c221a9c55fb71a23ff4e7bba3b794425?permalink_comment_id=4198425#gistcomment-4198425 where I made two improvements, one to return only the first match from the expansions (split on "/") and the second is to remove hyperlinks in the second which were showing up in the expansions, e.g. Scottish.

I also made one more improvement to convert 's from an expansion of "is, has, does, or us" to just "is". See the same link updated.

Here's the updated dataset:

{
  "a'ight": "alright",
  "ain't": "am not",
  "amn't": "am not",
  "'n'": "and",
  "arencha": "aren’t you",
  "aren't": "are not",
  "‘bout": "about",
  "can't": "cannot",
  "cap’n": "captain",
  "'cause": "because",
  "’cept": "except",
  "could've": "could have",
  "couldn't": "could not",
  "couldn't've": "could not have",
  "cuppa": "cup of",
  "dammit": "damn it",
  "daren't": "dare not",
  "daresn't": "dare not",
  "dasn't": "dare not",
  "didn't": "did not",
  "doesn't": "does not",
  "don't": "do not",
  "dunno": "don't know",
  "d'ye": "do you",
  "d'ya": "do you",
  "e'en": "even",
  "e'er": "ever",
  "'em": "them",
  "everybody's": "everybody is",
  "everyone's": "everyone is",
  "finna": "fixing to",
  "fo’c’sle": "forecastle",
  "’gainst": "against",
  "g'day": "good day",
  "gimme": "give me",
  "giv'n": "given",
  "gi'z": "give us",
  "gonna": "going to",
  "gon't": "go not",
  "gotta": "got to",
  "hadn't": "had not",
  "had've": "had have",
  "hasn't": "has not",
  "haven't": "have not",
  "he'd": "he had",
  "he'll": "he shall",
  "helluva": "hell of a",
  "he's": "he has",
  "here's": "here is",
  "how'd": "how did",
  "howdy": "how do you do",
  "how'll": "how will",
  "how're": "how are",
  "how's": "how has",
  "I'd": "I had",
  "I'd've": "I would have",
  "I'd'nt": "I would not",
  "I'd'nt've": "I would not have",
  "I'll": "I shall",
  "I'm": "I am",
  "Imma": "I am about to",
  "I'm'o": "I am going to",
  "innit": "isn't it",
  "Ion": "I don't",
  "I've": "I have",
  "isn't": "is not",
  "it'd": "it would",
  "it'll": "it shall",
  "it's": "it has",
  "Idunno": "I don't know",
  "kinda": "kind of",
  "let's": "let us",
  "loven't": "love not",
  "ma'am": "madam",
  "mayn't": "may not",
  "may've": "may have",
  "methinks": "I think",
  "mightn't": "might not",
  "might've": "might have",
  "mustn't": "must not",
  "mustn't've": "must not have",
  "must've": "must have",
  "‘neath": "beneath",
  "needn't": "need not",
  "nal": "and all",
  "ne'er": "never",
  "o'clock": "of the clock",
  "o'er": "over",
  "ol'": "old",
  "ought've": "ought have",
  "oughtn't": "ought not",
  "oughtn't've": "ought not have",
  "‘round": "around",
  "'s": "is",
  "shalln't": "shall not",
  "shan't": "shall not",
  "she'd": "she had",
  "she'll": "she shall",
  "she's": "she has",
  "should've": "should have",
  "shouldn't": "should not",
  "shouldn't've": "should not have",
  "somebody's": "somebody has",
  "someone's": "someone has",
  "something's": "something has",
  "so're": "so are",
  "so’s": "so is",
  "so’ve": "so have",
  "that'll": "that shall",
  "that're": "that are",
  "that's": "that has",
  "that'd": "that would",
  "there'd": "there had",
  "there'll": "there shall",
  "there're": "there are",
  "there's": "there has",
  "these're": "these are",
  "these've": "these have",
  "they'd": "they had",
  "they'll": "they shall",
  "they're": "they are",
  "they've": "they have",
  "this's": "this has",
  "those're": "those are",
  "those've": "those have",
  "'thout": "without",
  "’til": "until",
  "'tis": "it is",
  "to've": "to have",
  "'twas": "it was",
  "'tween": "between",
  "'twere": "it were",
  "w'all": "we all",
  "w'at": "we at",
  "wanna": "want to",
  "wasn't": "was not",
  "we'd": "we had",
  "we'd've": "we would have",
  "we'll": "we shall",
  "we're": "we are",
  "we've": "we have",
  "weren't": "were not",
  "whatcha": "what are you what about you",
  "what'd": "what did",
  "what'll": "what shall",
  "what're": "what are",
  "what's": "what has",
  "what've": "what have",
  "when's": "when has",
  "where'd": "where did",
  "where'll": "where shall",
  "where're": "where are",
  "where's": "where has",
  "where've": "where have",
  "which'd": "which had",
  "which'll": "which shall",
  "which're": "which are",
  "which's": "which has",
  "which've": "which have",
  "who'd": "who would",
  "who'd've": "who would have",
  "who'll": "who shall",
  "who're": "who are",
  "who's": "who has",
  "who've": "who have",
  "why'd": "why did",
  "why're": "why are",
  "why's": "why has",
  "willn't": "will not",
  "won't": "will not",
  "wonnot": "will not",
  "would've": "would have",
  "wouldn't": "would not",
  "wouldn't've": "would not have",
  "y'ain't": "you are not",
  "y'all": "you all",
  "y'all'd've": "you all would have",
  "y'all'd'n't've": "you all would not have",
  "y'all're": "you all are",
  "y'all'ren't": "you all are not",
  "y'at": "you at",
  "yes’m": "yes ma’am",
  "y'know": "you know",
  "yessir": "yes sir",
  "you'd": "you had",
  "you'll": "you shall",
  "you're": "you are",
  "you've": "you have",
  "when'd": "when did"
}