Some unfinished thoughts I ought to record somewhere:
Germany has sworn translators (as I call them – beeidigt, vereidigt – the terminology varies because the law is that of the Länder, not the federal government), but Britain doesn’t.
I sometimes read in a German translator’s English cv ‘In 19xx I was sworn in as a translator for the courts in North-Rhine-Westphalia’ or something like that. I would prefer ‘I was sworn as a translator’ or ‘I am a sworn translator’.
Is swear better than swear in?
Collins English Dictionary (my preferred one-volume one): swear in tr: to administer an oath to (a person) on his assuming office, entering the witness box to give evidence, etc.
Collins does not give this meaning for swear, only for swear in.
Garner’s Dictionary of Modern Legal Usage: swear is also sometimes used as a shorthand form for swear in – e.g. ‘Swear the witness.’
Oxford English Dictionary: swear 11 a To admit to an office or function by administering a formal oath.
(earliest usage 1049, whereas the first usage of swear in is in Evelyn’s diary in 1700)
It seems swear is OK then.
Another thing I am wondering is why, if swear in can refer to an office, I think it’s better to talk of swearing in a witness for one trial than swearing in a translator for an unlimited number of future occasions.