That's because the module title is something the administrator enters when he creates or edits the module. Similar to article or menu titles.
If you really need them in different languages, you can create multiple module instances and assign them to each language with each having the proper title.

I understand and I can change module titles, but when installing a clean Joomla, a certain number of modules is automatically published on the dashboard. Resulting in a partial English backend.

Or just use the automatic title option which is designed exactly for this

when installing a clean Joomla, a certain number of modules is automatically published on the dashboard. Resulting in a partial English backend.

Yep, that's because they are hardcoded in the SQL files.

Or just use the automatic title option which is designed exactly for this

Those only work for certain modules and the feature is disabled by default ?

Idea for a PR: Just wrap a JText around it to make them translateable... No?

We already have two ways to display the module titles in the admin in multiple languages - do we really need a third

We already have two ways to display the module titles in the admin in multiple languages - do we really need a third

No.

This should be closed as it is already possible

Set to "closed" on behalf of @Quy by The JTracker Application at issues.joomla.org/joomla-cms/23157