Claudine B. answered 08/01/19
French Native with a Master in French - Translator & Interpreter -
Here is a little bit of information that might help with understanding prononciation in Old French.
A combination of two or more letters that represents a single phoneme is called a digraph and is very conventional in Old French which changes the prononciation that we are used to.
Also, Old French uses the International Phonetic Alphabet which you can download to be able to write the words in Old French the accurate way.
Kind regards.