title: Django core: <django.utils.functional.__proxy__ object at ....> is not JSON serializable
body: <p>I'm using Django 1.8 and in some of my code I just do:</p>
  
  <pre><code>self.request.session['message'] = [
      _(u'Tag!'),
      _(u'Abt!'),
      _(u'Click here to hide this message')]
  </code></pre>
  
  <p>Then when the page refreshed I have this problem:</p>
  
  <pre><code>&lt;django.utils.functional.__proxy__ object at 0x04805F70&gt; is not JSON serializable
  </code></pre>
  
  <p>Of course I've googled for it, and I've read the <a href="https://docs.djangoproject.com/en/1.8/topics/http/sessions/#session-serialization" rel="nofollow">documentation</a> which says that "JSON supports only string keys" and "the JSON serializer from django.core.signing Can only serialize basic data types".</p>
  
  <p>Unless I'm wrong, arrays made of strings are basic data types. Moreover that code has been there for 6 months without a problem.</p>
  
  <p>What am I missing?</p>