During my PhD I've translated about a dozen papers into English, mostly from Russian. Google Translate and Yandex Translate did the actual translation (I would compare the two), but what they produce is not always intelligible or correct. On a few more important papers I went through the paper sentence by sentence to clarify the translation. It's not uncommon that I have to change certain phrases because the software translates a phrase literally when the equivalent is not a literal translation, for example. Sometimes I didn't know what the equivalent terminology was without research and guesswork. I also added footnotes as appropriate if I thought they would help the reader understand something which would not be clear if they were unfamiliar with the original language or research culture.

I would not be surprised if I spent over 100 hours on a particular series of 3 papers alone. I don't mind the time, as I enjoyed the process and learned a lot from it.

The good news is that I think the feedback I provided Google Translate improved the quality of the product's translation of scientific Russian, it is slowly getting better.