Why do so many non-native speakers from very different linguistic backgrounds seem to understand the term bitch as being a synonym for prostitute?-- I have never heard a native speaker use the former to refer to "a person who has sex with someone for money", and, as a native speaker myself, the word has absolutely no sexual connotations whatsoever. Furthermore, I am familiar with a few other languages, wherein the terms for "a female dog" and "prostitute" are often not the same, so it doesn't seem to be some sort of traditional L1 interference.
closed as primarily opinion-based by user140086, FumbleFingers, Hot Licks, Phil Sweet, Drew Jun 29 '16 at 17:03
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The British definition of bitch (from your link) includes both the following:
bitch noun (UNPLEASANT PERSON)
offensive: an unkind or unpleasant woman:
She can be a real bitch.
bitch noun (CONTROLLED PERSON)
offensive slang: someone who will do everything you tell them to do because you have complete control over them
Those meanings are not included in the corresponding American definition, so I assume that it is not used in those ways in American English.
I have often heard (on TV) a prostitute being called a bitch, but have always understood that to be a comment on the person's character, and not a synonym for prostitute. However, it is easy to understand that a non-native speaker might assume the two words to be synonyms.
I would wager it's because a lot of languages lack an accurate translation for "bitch". I know French, Spanish and Portuguese don't. As is the case with those languages, most insults to women are different ways of saying "whore", "slut", or, simply, "prostitute". "Bitch" is actually a very specific concept, if you think about it, and most people wouldn't be able to give an exact definition of what a "bitch" is. This, of course, is a nightmare for translators, who figure it's fine as long as the audience it's being translated to knows it's meant as an insult.