how well does madame eglantine really speak french

Chaucer writes in the Prologue:

And fair she spoke her French, and fluently,

After the school of Stratford-at-the-Bow,

For French of Paris was not hers to know.

So, while it is interesting that Madame Eglantine spoke her French "fluently" (perhaps tongue-in-cheek), it is clear that Parisians would not think so.

The Prioress, Madame Eglantine, is a character full of denial. Though she is a nun whose duties should be pledged to God, she certainly considers herself a lady first. She speaks bad French (many of her words are mispronounced) ate and dressed very carefully, and wears a brooch that says "love conquers all." She also cares deeply for animals, bringing several along with her on the pilgrimage. Her lady-like behavior seems to stand in direct contrast to the ways of a good Nun. This is Chaucer's first criticism of religion, a theme he returns to throughout the poem.