Not fluid, but I love paleography and got interested in scribal abbreviations and incunabula. Much of this is from Wikipedia.
Like in English, bad spelling betrays the pronunciation which changes over the decades.
The scholars complained all the time about the plebs and peasants talkin' like a bunch o' rubes gitt'n all them words wrong.
Thuh kid withowt uh dikshuneree wil spel it how it sownz, and yu can fynd it on sum grufeedee in Pompey.
We can make a lot of guesses as to what happened:
•Vowel + n + (s/f) turned into nasal vowel + (s/f). "vocans" turned into vocãs.
•A word with two or more syllables would lose its final-m "secundam" turned to "secundã".
•a qu-sound before an o or a u would lose the u. "Quondam" turned into "condã"
•H was dropped. In the Catholicon it isn't even considered a letter, but an "aspiration mark." "mihi" would need to be spelt "michi" or it would be pronounced mî.
•most ae and oe turned into monophthongs.
In Greek, αι became ε and ε became "ε ψιλον" (plain e). οι became υ and υ became "υ ψιλον" (I think it was first pronounced like a ü and eventually another i).
Latin later did something similar. If it was kept a diphthong, you put a trema over the other vowel like in greek. ære for bronze, aëre for air.
Eventually both were often spelt with a little tail on the ę to save precious parchment, and quit caring which was which. "Cœlum" was written "cælum".
•when it made speaking easier, i or e before another vowel would turn into a consonant i and sometimes stress its vowel. "cuius" turned into "cujus".
•I think a lot of "vi"s in the middle of words dropped. Novisti turned into nôsti.