{% load i18n %}
<h3>{% blocktrans with filter_title=title %}By {{ filter_title }}{% endblocktrans %}</h3>

<ul>
  <li>
    <form action="" method="get">
        {% if choices.0.form %}
          {{ choices.0.form.as_p }}
        {% else %}
          {{ spec.form.as_p }}
        {% endif %}
        {% for k, v in choices.0.params.items %}
          <input type="hidden" name="{{ k }}" value="{{ v }}"/>
        {% endfor %}
        <div class="controls">
            <input type="submit" value="{% trans 'Filter' %}">
        </div>
    </form>
  </li>
</ul>

Add range filter widget template
Add range filter widget template