Craft 2: Locale throwing 404 in frontend
However, when I try to access any page apart from the homepage in my
  2nd locale in the frontend I get a 404 error.


Could it be, that as a result of your settings, URL's for /en do not get rewritten correctly? I don't know how you redirect SEO-friendly urls, but most of the times (at least in my life) if accessing all pages but the homepage fails, it has something to do with URL rewriting.