[Answered ]-How to detect language with tag in Django CMS

Actually, you’re thinking it wrong. Django supports translation, in Python code and in the templates.
The Django Translation documentation gives advice on how to do this.

You create a template with

{% load i18n %}
{% trans "Hello" %}

“Hello” will be translated to bonjour once you set it up.

You will need to activate I18N in your project settings, then call

manage.py makemessages

to create a .po file for your project. Once you create the translations for the .po file, type something like

manage.py compilemessages

The actual way of doing things is a bit more difficult than this but is described properly in the docs.