A rant or a raunt

Something I often find surprising is how otherwise well-informed people, when called on to read Middle English – as well-informed people so often are – will fall into a cultural cringe when faced with a word of French origin such as 'gentil' and come out with something like [jontil], or, worse still, [ʒontil] (excuse my phonetics – they're the symbols I find convenient, and pretty transparent, I would have thought).
A quick breeze through any of the Canterbury Tales would make it clear that Chaucer doesn't rhyme French e+nasal+consonant with French a+nasal+consonant: e.g. 'apparence' wouldn't rhyme with 'da(u)nce)' – but on the other hand French e+nasal+consonant does rhyme with OE-derived e+nasal+consonant: thus 'rente' with 'wente'.
The fact is, of course, that the vowels e and a before a nasal didn't merge in northern and western French as they did from about C11 in central French – and the English French vocabulary owes more in this respect to the provincial pronunciation.
Now it's true that we do have loans from central French that show the merger: e.g. 'ensaumple', but in such cases the resulting vowel is spelt a(u) in English. There's also the complicating factor that in Anglo-Norman many verbs were transferred to the -er conjugation – hence 'defendant' rather than 'defendent'. In the case of 'jaunty' from central French 'gentil' the lack of the final consonant  in the English word is enough to mark it as a late borrowing.

In mainstream English, however, French e+N+C (you understand the symbolism) gives English e+N+C (and I'd guess that for semi-learned forms like 'sentence' the current rponunciation of Latin would have played a role. French a+N+C, on the other hand, gives a+N+C, or when stressed au+N+C. Hence French 'lande' > Modern English 'lawn'.

One might reflect that French i+N+C also gives English i+N+C, e.g. 'prince'.

So, Middle English 'gentil' should for preference be sounded as [jentil] – though it's always possible that a 14th century English person wanting to show off their 'French of Paris' might introduce the foreign sound.

See, on this subject, Pope: From Latin to Modern French.