I can't find who actually said English is mispronounced French, now. It was probably used in the context of taking a dig at England.
I think it may have been Daniel Defoe. He certainly railed against English pretensions of ethnic and linguistic purity in his poem
A True-Born Englishman, in which after listing the diverse ethnicities who'd overan Britain throughout history he rhymed:
[quote From this amphibious ill-born mob began
That vain ill-natured thing, an Englishman.
The customs, surnames, languages, and manners
Of all these nations are their own explainers:
Whose relics are so lasting and so strong,
They ha' left a shibboleth upon our tongue,
By which with easy search you may distinguish
Your Roman-Saxon-Danish-Norman English][/quote]