on a multi-language site 'Entity translation' prefs don't show 'node' option
I just recently had this problem and after 6 hours of searching for a solution I tried the following, which seems to work for me:

Without having Entity Translation installed first update Internationalization (i18n) to the latest version. Then setup the necessary submodules like "Field translation" that you need from Internationalization.

After this is all done then download and enable Entity Translation, go to Entity Translation settings under /admin/config/regional/entity_translation and enable "Content" under "Translatable Entity Types". 

If you haven't configure any of your content types to be translatable with field translation (under publishing options) you won't see anything here.
So after doing this for at least one of my content types this page showed the Content tab to add the correct settings for each content type.