Do non-English academic journals pay for a translated paper?
I think you'd have a better chance of getting more reliable information if you go to popular online forums for translators like ProZ and TranslatorsCafé, where you can talk to professional translators and browse job ads. A very quick search already gave me one recent (but already closed) ad that seems to be looking for a translator for an academic journal:

http://www.translatorscafe.com/cafe/job146043.htm


  I am currently in search of French to English Translator with a mathematics &amp; engineering background to translate an academic journal.


Also, AMS seems to have a list of translated journals here:

http://www.ams.org/msnhtml/trnjor.pdf

Anyway, there seems to be a demand for that kind of job, so you might be able to find a job if you know where to look. So, maybe the question is more about how to become a professional translator (and find jobs) than about academia.