Rhyming slang is a riddling tradition comparable to skaldic verse. Anyone is free to innovate within it. For instance, where once a stupid fellow was called a berk (shire hunt), he may well now be a James Blunt, which has a sort of delightful circularity to it.
It’s also conducted in the language from which it originates. That said, sometimes we use German terms unneccessarily. In most instances where a germanism is adopted, it makes sense to - there is no English equivalent to ‘Schadenfreude’, although most English speakers fail to pronounce the final ‘e’, and Zeitgeist would be clumsily rendered as ‘the spirit of the times/age’. In fact, there are some terms such as ‘Fremdschaemung’ (Embarrassment felt on behalf of another or a stranger) which we could benefit from. However I’ve noticed a tendency amongst some people to use the term ‘verboten’ in otherwise English sentences, despite the perfectly serviceable and almost identical ‘forbidden’ already existing in our language. I don’t know whether this is an attempt to appeal to racist German stereotypes (Germans are authoritarian so verboten is even more forbidden!) or simple pretentiousness after the manner of French malapropism in the 1980s, but it is vastly annoying.
