Conversational Middle English would have varied a lot in its sound and its vocabulary depending on where you grew up and where you lived, even for people who were capable of reading and writing it as well as speaking it -- one of the ways we can see this reflected is in the writings of Middle English poets who aren't Chaucer, to the point where it's one of several tools for figuring out which anonymous authors wrote which poems based on where they were likely from. (There's an awesome thread on how intense this variation can be: "How is it that I can mostly read "The Canterbury Tales" in the original, but "Sir Gawain and the Green Knight," written at roughly the same time and in the same country, is mostly unintelligible?" , where /u/sunagainstgold talks about Chaucer and the Pearl poet.)

Latin and French were both still elite languages within England -- Richard II and most of his relatives would have been conversant in French, for instance, and Chaucer's own Prioress speaks French like a cultivated Englishwoman, not because she's actually visited France:

And frenssh she spak ful faire and fetisly,

After the scole of stratford atte bowe,

For frenssh of parys was to hire unknowe.

Middle English as a vernacular language was more egalitarian than either of these, but it still had tons of regional variation, and regional dialects that can look drastically different from Chaucer's -- Chaucer's London-and-London-adjacent dialect usages have the retroactive advantage of being rooted in the dialect pool that would become the standard for "standard English" later on, but there really wasn't a standard for "good English" yet, or for what English words marked out formality and propriety. (If an author wanted to evoke legal or liturgical language, they might dip into Latin.) A Middle English speaker who lived her whole life in Cornwall would sound really different from one who spent his whole life in Cumberland, or Cheshire, or Norfolk. We can tell a lot about how Middle English sounded when it was spoken by looking at regional spelling variations, since there was no one standard spelling of any given word, even proper names. We can tell a lot about how Middle English was used in a region by commoners and educated people alike by also looking at documents with fewer pretensions to being "literature", like legal documents or even cookbooks. Tools like the Middle English Compendium's HyperBibliography of Middle English texts can be searched by scribal dialect to see a variety of texts written by individuals of certain regions, and by comparing these texts we can get an idea of how different people of different regions and classes might have talked.

Even an individual who couldn't herself read or write could dictate a document to a local scribe, so it's possible to catch some fleeting glances at what conversational or less-formalized Middle English sounded like from documents whose purpose wasn't necessarily to sound impressive. There are also class and region cues within a particular author's choice of vocabulary -- are they using French-influenced words? Scandinavian-influenced words? Both? Neither? But overall, the range of regional variation even in written, "literary" Middle English suggests to me that there wasn't a huge push yet to standardize written dialects and vocabularies along regional/class lines, so we can still get some useful info about what conversational Middle English speech sounded like in a particular region from written Middle English from that region.

The use of rhyme and alliteration in the writing of Chaucer and his contemporary poets is one thing we can pretty much assume common people didn't use every day -- the poetic devices of Chaucer, Gower, the Pearl poet, etc. were literary inventions, purposefully conforming statements to meter and rhyme schemes/alliterative schemes rather than presenting flat prose. But commoners literate and otherwise would have already been familiar with the use of rhyme for artistic effect -- songs and verses, rhymes as aids to memory, and so on. The most high-profile instance of rhyming verse used as a device in an otherwise non-rhyming work might be "When Adam dalf and Eve span, / Who was thanne a gentelman?" associated with the radical priest John Ball and the peasant uprising of 1381. (Ball is a priest, but he's supposed to be speaking to the common rabble. Whether or not his speeches actually occurred as they were recorded is debatable, but that particular verse seems to have made an impact on the populace, and remained in widespread circulation even after the uprising was quashed.) But there's a lot to suggest this couplet existed before Ball invoked it in a sermon -- that it was a common proverb (emphasis on the "common") in the preceding decades, and Ball was invoking a slogan whose power and potency came from the fact that it was already known to its audience. This evoked a saying cited even earlier, cited by authors as having already been in broad circulation:

When Adam delf and Eve span,

Spire if thou wil spede,

Whare was than the pride of man,

That now merres his mede?

Of erthe and slame, als was Adam,

Maked to noyes nad nede,

Ar we, als he, maked to be

Whil we this lyfe sal lede

This is hardly plain-spoken conversational English -- it's written in rhyming meter and uses poetic structures, people didn't go around speaking in pithy rhyming aphorisms when they were expressing their proto-democratic grievances with the nobility -- but it's not elevated literary language of the elite, either. Middle English as spoken by commoners and laypeople didn't follow the literary forms that have survived in literature from this period, but then again, neither did the day-to-day conversations of noblemen/noblewomen and clergy. I don't think the vocabulary of non-clergy, non-upper-class speakers was so different from their social betters that the groups couldn't have understood one another in conversational speech, at least if they lived in the same regions as each other. We can get a sense of how Chaucer sounded when he was writing in "plain" prose from his Treatise on the Astrolabe -- it's not conversational, being structured as a treatise outlining the different parts and functions of an astrolabe, but it's not poetry either and it likely sounds more like what Chaucer himself sounded like in regular conversation than the Canterbury Tales do.

Random postscript: I've been puzzling over regional and class differences in Middle English recently after running into a quite scornful reference from the Kenilworth Chronicle to Richard II making conversation with his bodyguard of Cheshire archers "in their own mother language" --

Et in tantam familiaritatem domino regi annectebantur ut eidem in materna lingua audacter confabularentur [And they were attached to their lord the king in such great familiarity that they shamelessly chatted with him in their mother tongue]: "Dycun, slep sicurly quile we wake, and dreed nouzt quile we lyve sestow: ffor zif thow haddest weddet Perkyn douzter of Lye thow mun well halde a love day with any man in Chester schire in ffaith!"

• (From "Pearl in Its Royal Setting: Ricardian Poetry Revisited", John M. Bowers, which also talks about the Cheshire dialect of the Pearl poet.)

This is one of those quotes that kind of haunts scholarship about the historical Richard II, at least for me. The chronicler goes on to remark that familiarity breeds contempt, but contempt from whom? Is the objection that speaking with these men at all is beneath a king's dignity, or is it speaking with them in Middle English and not in French or something, or is it the use of an un-courtly Cheshire dialect, or is it the fact that the statements' content is so familiar that it's inappropriate? (Sir Piers/Peter de Leigh was a Cheshire gentleman and a high-profile supporter of Richard II in the region who would ultimately end up executed in the attempted counter-coup of 1399. I honestly don't know what a love day would have entailed in this context.) This is such an odd and affectionate declaration that I'm curious where the chronicler got it from or if he invented it outright as an example of the kind of liberties the Cheshire rabble were taking with their sovereign. It would probably help a lot if I could figure out how "sestow" is functioning here -- "dread not while thou see-est us live" is the most I can make of it and that sounds truly monstrous!