Where does “pardon my français” come from?

pardon my français (English) comes from English francais, from French français, from Middle French françois, from Old French françois, from Old French -ois, from Latin -ensis, from Latin arvum, from Latin colō — to turn.

Ancestry of “pardon my français”, step by step

pardon my français traces back through two separate lines of ancestry.

via English francais

StepLanguageWordMeaning
1EnglishfrancaisFrench
2FrenchfrançaisFrench; Franco-American or Francophone
3Middle FrenchfrançoisAlternative form of françoys
4Old FrenchfrançoisFrench; the French language
5Old French-oisused to form nationalities; used to form names of...
6Latin-ensisOf or from
7Latinarvumfield; farm land
8Latincolōto cultivate the land, till, tend, take care of a field or garden
9Latinquelō
10Proto-Italickʷelōto inhabit
11Proto-Indo-Europeankʷéleti
12Proto-Indo-Europeankʷel-to turn

via English pardon my French

StepLanguageWordMeaning
1Englishpardon my FrenchTo excuse the speaker's frankness of expression or profanity
Every word from Proto-Indo-European kʷel-Every word from Proto-Indo-European kʷéletiEvery word from Proto-Italic kʷelō