Green’s Dictionary of Slang

Frenchman n.

1. a scholar of French.

1670		C. Cotton Espernon Preface: The greater part of them being better Frenchmen, than I pretend to be [OED].
1828		Bentham in Works (1843) I 247: The subject was not without its difficulties; the language French: I am but a sorry Frenchman now; I was, I imagine, not quite so bad an one then .

SE in slang uses

In compounds

Frenchman’s parole (n.) [play on French leave n. (1)]

an escape from prison.

1955

‘Blackie’ Audett Rap Sheet 96: That was the set-up when Frank gave himself the Frenchman’s parole and taken it on the lam.