UnicodeEncodeError when using German translation

[RalfJung]

When accessing current master dudel in German, I sometimes get UnicodeEncodeError. It seems that the codec is not set up correctly everywhere.

One way to reproduce this is to do make seed, and then go to http://127.0.0.1:5000/test-autodelete.

Here's the full backtrace:

Traceback (most recent call last):
  File "/home/r/src/dudel/dudel-env/lib/python2.7/site-packages/flask/app.py", line 1836, in __call__
    return self.wsgi_app(environ, start_response)
  File "/home/r/src/dudel/dudel-env/lib/python2.7/site-packages/flask/app.py", line 1820, in wsgi_app
    response = self.make_response(self.handle_exception(e))
  File "/home/r/src/dudel/dudel-env/lib/python2.7/site-packages/flask/app.py", line 1403, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/home/r/src/dudel/dudel-env/lib/python2.7/site-packages/flask/app.py", line 1817, in wsgi_app
    response = self.full_dispatch_request()
  File "/home/r/src/dudel/dudel-env/lib/python2.7/site-packages/flask/app.py", line 1477, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/home/r/src/dudel/dudel-env/lib/python2.7/site-packages/flask/app.py", line 1381, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/home/r/src/dudel/dudel-env/lib/python2.7/site-packages/flask/app.py", line 1475, in full_dispatch_request
    rv = self.dispatch_request()
  File "/home/r/src/dudel/dudel-env/lib/python2.7/site-packages/flask/app.py", line 1461, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/home/r/src/dudel/dudel/views.py", line 372, in poll_overview
    return render_template("poll/overview.jade", poll=poll)
  File "/home/r/src/dudel/dudel-env/lib/python2.7/site-packages/flask/templating.py", line 128, in render_template
    context, ctx.app)
  File "/home/r/src/dudel/dudel-env/lib/python2.7/site-packages/flask/templating.py", line 110, in _render
    rv = template.render(context)
  File "/home/r/src/dudel/dudel-env/lib/python2.7/site-packages/jinja2/environment.py", line 969, in render
    return self.environment.handle_exception(exc_info, True)
  File "/home/r/src/dudel/dudel-env/lib/python2.7/site-packages/jinja2/environment.py", line 742, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/home/r/src/dudel/dudel/templates/poll/overview.jade", line 1, in top-level template code
    extends poll/BASE.jade
  File "/home/r/src/dudel/dudel/templates/poll/BASE.jade", line 1, in top-level template code
    extends BASE.jade
  File "/home/r/src/dudel/dudel/templates/BASE.jade", line 13, in top-level template code
    - assets "css_all"
  File "/home/r/src/dudel/dudel/templates/poll/BASE.jade", line 7, in block "header"
    header.poll
  File "/home/r/src/dudel/dudel/templates/poll/_properties.jade", line 4, in top-level template code
    span.content= content
  File "/home/r/src/dudel/dudel/templates/poll/_properties.jade", line 2, in template
    li(title=(title + (": #{hover}" if hover else "")))