How should I cite two different translations?
Cite each translation where you use it, just as you would if they were different works.  

To ease any confusion on the part of the reader, however, it would likely be a good idea to also:


In your introductory material, note that you are using two different translations and why your are doing so, and
Call attention in the prose when you use the unusual translation, and why you have chosen to use that one instead in this circumstance.