Well, if they can get through to Google Support, what can a mere Human do to hide? ;)
On a more serious note, if you're going to that level of security, you're probably using something like TOR anyway (otherwise they simply ask the site the text was posted on for the IP). Additionally, you can use multiple services for each translation, obscuring the trail further. Good luck getting that data from Yandex.
Lastly, I'm not sure whether Google (and others) really log every sentence entered, but as described before, you can easily avoid that. Or read the privacy policy.
On a more serious note, if you're going to that level of security, you're probably using something like TOR anyway (otherwise they simply ask the site the text was posted on for the IP). Additionally, you can use multiple services for each translation, obscuring the trail further. Good luck getting that data from Yandex.
Lastly, I'm not sure whether Google (and others) really log every sentence entered, but as described before, you can easily avoid that. Or read the privacy policy.