Cherubini’s Medea, in the 1909 Italian version being used by the COC, got there by a fairly circuitous route. Euripides 5th century BCE tragedy and Seneca’s 1st century CE play inspired a French verse version of 1635 by Thomas Corneille which was turned into an opera by Marc-Antoine Charpentier in 1693. In 1797 a version with music by Cherubini to a libretto by François-Benoît Hoffman; retaining much of Corneille’s version as spoken dialogue, premiered in Paris. In 1909, for the Italian premiere at La Scala an Italian translation with added recitatives was used and that became, more or less, the standard version for its rare 20th century revivals (most notably in the 1950s with Maria Callas) and that’s the version being given at the COC with Sondra Radvanovsky in the title role. Understandable really. It’s hard enough to find a cast that can do justice to the music. To expect them also to be expert at declaiming Alexandrines en français is probably expecting a bit too much.
