Despite Madame Eglantine’s “fluent” speaking skills, her French cannot be called good. It is because she is not aware of Parisian French and would likely be misunderstood by actual French people.
In the General Prologue, Chaucer introduces Madame Eglantine in an ironic way. He touches upon her traits, habits, and skills, such as the knowledge of French. The author first describes her modesty and kindness. Then, he mentions that “she spoke French fairly and fluently, after the school of Stratford-at-the-Bow.” At first sight, it seems that he expresses his admiration with the way of how the nun speaks French.
Yet, fluency does not necessarily involve proper pronunciation. In the next lines of the prologue, the author provides more clarity. Turn out that Parisian or Metropolitan French was something new to Madame Eglantine. She had a strong accent, even if her understanding of grammar was adequate. Since poor pronunciation can make words almost incomprehensible, Madame Eglantine’s French cannot be called good.
The prioress who learned French gives the reader a hint that Eglantine’s knowledge is flawed. She did not learn French from native speakers who would introduce her to the basics of pronunciation and explain the unique features of standard or Parisian French. Today, it is known that foreign languages are best learned through immersion in relevant language environments. Madame Eglantine clearly had no such experiences. Thus, the appraisal of her foreign language skills should not be understood literally.