How do I add an English Wikipedia article for translation into Hebrew?
I don't think this capability will be added to Duolingo; the "Immersion" tab has, alas, ceased development and is not available for many (probably most?) languages.
While some people have... ahem... circumvented this lack of development, it's more or less an unintended function which therefore might potentially break or be subject to a crackdown (In fact I currently can't swear that it hasn't, because I haven't been keeping up with the discussion boards). The right-to-left aspect of Hebrew and/or the different character set may not function well within the Immersion set up since they were not intended to be supported. (That said, I've seen one of those unofficial Russian to English translations work okay, so character sets might not be troublesome.) Also, I don't believe there's a Hebrew-English course that would coordinate with such translation, so I'm not sure if the language pair would be selectable.
...if you remained determined, you might be able to find someone who knows how to do that unofficial uploading by searching for a discussion thread listing such articles. I think Swedish was one of the languages it had been done for
(edited in hopes of achieving intended formatting. oh well, I thought it was possible but now I can't find out how to strikethrough text if it is)