Steven Zahm@ Stephan
re: I thought that it was necessary to create the directory wp-content/languages/connections and to place those files( connections-fr_FR.mo and .po files )coming from Connections/languages in it ?
No, you only do this if you are using your own custom translation and not the one that is supplied with Connections.
Since Connections does not come with PO files because translations are managed on Transifex, I do not know where those files came from that you are using… perhaps they are empty which would explain why the admin page are in English.
My suggestion… Deactivate and delete Connections and reinstall and activate it. Any data you have add to Connections will be safe. Also delete the files in the ..wp-content/languages/connections/ folder so they are not used. They will override the files that come with Connections if they are there.
The will restore Connections to it original state.
Hope that helps.