Those translations are rather bad, at least for languages I use. It appears to use the same algorithm as the free translate service.
Developers have option to buy professional translation inside Play Store, and some probably do it for mainstream languages. I'm not sure if you can tell if developer has used it (except by judging the quality of translation)
From the link I posted, "There will be a note above the translation explaining that the translation has been done automatically, and an option to return to the default language." - so presumably if that's not present it was professionally translated.
The article talks about the Chrome webstore. I was replying to a comment about the Play store so I used a link for that, but I mentioned Chrome also because the article of this discussion is about auto-translated Chrome store descriptions.
Under the subheading "Can Google Translate Be Used To Create Auto-Translated, Non-Spam Content?" they discuss a chrome webstore app [0] and compare the Google translate version to the auto-translated version. Indeed the proof is in the article too, you can change your language in the settings (picture in the article) and see the descriptions translated.
"purchase professional app translations through the Google Play Developer Console" "select a professional translation vendor"
That said, translation vendors tend to just translate automatically first and then have a human clean it up.