There is another mechanism.
Frenchmen with little education speak American English. (Or no English at all) Highly educated Frenchmen use British English. It is all to do with status.
Even if my English is a potpourri of British, American and other variants, whenever aware of it I will use British spelling and vocabulary. Not to impress the English speakers, or to make myself better understood to them - but to distinguish myself as a person of education and higher cultural norms to other non-native speakers.

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