[Answer]-Does Django try to translate template variables?

You can have variables in blocktrans blocks, but you can’t access object attributes, as you are attempting with user.username. You need to bind those to local variables, as per the documentation:

{% blocktrans with amount=article.price %}
That will cost $ {{ amount }}.
{% endblocktrans %}

EDIT: Sorry, I just noticed I misread your question, you do mention local binding. But then that’s your answer. The example you show from django core uses site_name, not site.name.