Citing unofficial translations One of the references I use in my text is paper A.
However, I've actually read an unofficial, unpublished translation B which can be found online.
The translation uses more modern definitions/terms and corrects some errors.
How should I properly reflect the usage of the translation in my bibliography?
Currently, I use the original reference together with a note in the bibliography which explains the situation:

[reference A entry] Translated unofficially by translator as title
B, year B. Translation available online at url B.

Note that the original author did not give permission to publish the translation.
From the Translator's preface:

[author] has asked that all republication of any of his works (in original or translation) be ended.
He has not actually invoked copyright (which, as stated above, he does not believe in), but asked this as some sort of personal privilege.
Citing both, as you currently have, is fine and provides good a good indication to readers who are unfamiliar with this paper.
With regards to the fact that the translation was not permitted by the author, that is strictly not your problem. Copyright doesn't apply to people who are viewing or otherwise using the copied content, but to its distributor (i.e. the translator in this case). This would be no different to me simply sharing the URL of an unofficial stream of a football match (where the official source is a payed TV channel) with a friend --  I would never get into trouble for this, only the website hosting the stream could.