Wagtail, tu aurais pu t'appeler Swagtail.

block_tags.py

# templatetags/block_tags.py

import re
register = template.Library()

@register.inclusion_tag('tags/embed_tweet.html', takes_context=True)
def tweet_embed(context, url):
    return {
        'url': '{}'.format(url),
        'request': context['request'],
    }

blocks.py

# blocks.py

from django.utils.translation import ugettext_lazy as _
from wagtail.wagtailcore import blocks

class TweetBlock(blocks.StructBlock):
    url = blocks.URLBlock(help_text=_('Tweet URL'))

    class Meta:
        icon = 'twitter'

embed_tweet.html

<style>
    .twitter-tweet {
        display: block;
        margin: auto;
    }
</style>

<blockquote class="twitter-tweet">
    <a href="{{ url }}"> Chargement du tweet</a>
</blockquote>

<!-- Don't forget to insert the twitter script ! -->
<!-- <script async src="//platform.twitter.com/widgets.js" charset="utf-8"></script> -->

models.py

# models.py

class BlogPost(Page):
    cover_picture = models.ForeignKey(
        'wagtailimages.Image',
        null=True,
        blank=True,
        on_delete=models.SET_NULL,
        related_name='+',
        help_text=_('Choose the cover picture')
    )

    body = StreamField([
        ('paragraph', blocks.RichTextBlock(
            label=_('paragraphe'),
            icon='pilcrow',
            help_text=_('Insert a paragraph'),
        )),
        ('tweet', TweetBlock(
            label=_('Tweet URL'),
            help_text=_('Insert a Tweet')
        )),
    ])

    content_panels = Page.content_panels + [
        ImageChooserPanel('cover_picture'),
        StreamFieldPanel('body'),
    ]

    search_fields = Page.search_fields + (
        index.SearchField('body'),
    )

models_simple.py

# models.py

class BlogPost(Page):
    cover_picture = models.ForeignKey(
        'wagtailimages.Image',
        null=True,
        blank=True,
        on_delete=models.SET_NULL,
        related_name='+',
        help_text=_('Choose the cover picture')
    )

    body = RichTextField()

    content_panels = Page.content_panels + [
        ImageChooserPanel('cover_picture'),
        FieldPanel('body'),
    ]

    search_fields = Page.search_fields + (
        index.SearchField('body'),
    )