I remember a true story of a friend of mine from the prude 1960s.
A 12 yo German girl visited a French family for holiday. During lunch, she was invited by the lady to take a refill of her dish. She refused politely, translating the colloquial German phrase "Nein danke, ich bin voll" (verbatim: No, thank you, I am full) to "Non merci, je suis plain!" (plain = full)
Embarrassed silence at the table which can be explained by the re-translation:
"Je suis plain" is colloquial for "I am expecting"
Words can be false friends ;)