Hi,

I would like to edit the text message when public user register to get an email link and be able to answer to the survey. This text can't be edited via the "email template editor" (?!) but it's located in locales files (locale/fr/fr.mo in my case).
How edit a .mo file ?

Thanks

You need to edit the .po files.
You can find instructions how to create or change language files in the manual.
manual.limesurvey.org/Translating_LimeSurvey