The article which I am translating into English quotes extensively from translated versions of works by English authors (e.g. a Spanish translated version of Philip Pettit’s ‘Republicanism’). As the translator, do I translate these quotations into English myself, or do I need to find Pettit’s original English words? I’m not sure, because the latter would mean quoting from a text (the original, English version of ‘Republicanism’) which the author of the article I am translating did not read... In which case do I simply do the former but make very clear in the in-text references that I am quoting from a translation?
In my research I need to cite a work by a Russian author, Gnedenko, say, who, for reasons unknown to me, published in French, in an American journal. There being no published translations of the original French (if he really did write in French, which I doubt), I have translated the French into English. When I need to quote I will use my words followed by "(Gnedenko [reference] - my translation)".
In practice, in my subject, statistics, Gnedenko's exact words matter much less than his ideas, and if I wished to cite another author who studied Gnedenko in translation it would not matter much which language that author had read the paper in.
If in your subject it really matters what language other writers have read a paper in, then you have no alternative but to quote those words, in whatever language was used. You may provide your own translation, identified as such.
The point is that you must leave no doubt in your readers' minds as to where the words you cite came from.