As mentioned in Translation software/services:
I use DeepL, but it seems to be going downhill a bit. I’m not sure how private it still is, but, for example, it now only lets you translate 1500 characters instead of 5000. And their mobile app, which is the only place you can do image translation, is of course non-free.
In addition to those problems though, they’re also trying really hard to push an account on your. For example, they won’t let you translate documents without one.
Is this account private (if DeepL is even private in the first place)? As in, can I create one and be safe in the knowledge that am I not giving up my privacy?
Well the data is transmitted to their servers in any case, whether you use it with an account or not. What happens afterwards, there is no way for us to know and therefore, as with any translation service offered by someone over the internet that runs on their servers, it is not strictly private.
Actually private translation would need to happen on your own devices without your input data being sent to someone else’s device first.