Use the Jinja i18n extension for translation

[haltode]

Currently we have this sort of code for small translations:

haltode.fr/templates/default.html.jinja

Lines 16 to 20 in 2df4e24

	{% if metadata['language'] == 'fr' %}
	<p class="metadata">Publié : {{ metadata['published'] }} · Modifié : {{ metadata['modified'] }}</p>
	{% else %}
	<p class="metadata">Published: {{ metadata['published'] }} · Modified: {{ metadata['modified'] }}</p>
	{% endif %}

This is totally reasonable for one or two translation block (as it is currently the case), but it might be a better idea to use Jinja i18n extension instead. Especially if in the future there are more translations to be done.