Translation quality is, in general, terrible. By "terrible" I mean not nearly good enough for philosophy where some precision and detail matters. I've read 5 different translations of Xenophanes' fragments. They are all significantly different, and they change the meaning.

BTW I'm not even sure if an English translation of Xenophanes existed yet when Popper learned Greek. Lesher's book was published in 1992. Of course Popper was fluent in German, but the German translators are in general significantly worse, and the German language is not good for philosophy. Once Popper learned English he stopped doing philosophy in German saying it was much worse for it.

Popper did his own translations of some text and published criticisms of other translation which had got it wrong. He gives good arguments about why he has it right which are persuasive. Some of the people replied, and you can read their view of the matter and judge for yourself who had it right (Popper :).

To do good translations of philosophers, you have to not just know the language but also have some understanding of the philosophy. That's the main reason Popper was able to do better than other translators who knew the language better than him. Popper came up with good explanations about what the people were trying to say, while others focussed on words too directly.

About the dog, you're correct that on the theory that both people and animals do induction all the time it must have predated Aristotle. So if Popper is wrong about his major ideas, he's wrong about this one too; but if not then you're argument wouldn't hold for this. On our theory that induction is a substantive philosophical idea, not ever done by anyone but merely a misconception, then it was invented. And Aristotle is the best candidate for who did it, as Popper explained.

One thing to consider is: if induction predates aristotle, which philosophers predating aristotle are in the inductivist tradition? In my reading, they are all different in their attitudes, assumptions and outlooks. Xenophanes is a good example of this (who Aristotle disliked). If you can't find any induction in the presocratics, then saying it was popular since prehistory wouldn't really make sense.

The dog is just enacting programs encoded in its genes by evolution (uniquely among animals, dog genes contain knowledge of human memes). Dogs can't create knowledge, humans are the only animal that have that capacity, and the evolutionary process that created the knowledge in a dog's genes is not an inductive process.

Popper learnt ancient Greek because he knew that translations are often wildly inaccurate and they are inaccurate because all translations are interpretations. He liked to get his facts correct.