Fix language issue in email sent to authors

[cdparra]

It seems that when someone who has never registered is invited to share in a proposal, that person receives the email notification in English. We think that this occurs only when the recipient has never registered. Can we make the default language of the email notification the same as the language of the campaign?

The code already tries to use the assembly or campaign language but for some reason this is not working.

[yolile]

This could be because:

• The lang for the users is English
• The lang for the WG is English