How may I help to have french holiday after 2025 in Ganttproject ? or maybe someone is already in charge to update this point ?
Typing the data in, might it be an option.
That is what I did for holidays in Spain.
I was wondering how to make the new file for France, so that it can be included in the next update. Or other option : is it possible to download such file instead of type the data in every projet as @malcaraz suggest ?
Good enhacement request! Something available as [MS Outlook has yet]. (Add holidays to your calendar in Outlook - Microsoft Support)
The file is here: biz.ganttproject.app.localization/i18n_fr.calendar at master · bardsoftware/biz.ganttproject.app.localization · GitHub
(raw downloadable version: https://raw.githubusercontent.com/bardsoftware/biz.ganttproject.app.localization/master/src/main/resources/calendars/i18n_fr.calendar)
I am not sure that i clearly understand what did you mean as “is it possible to download” though.
If you add the holidays beyond 2025 and send us a new version, it surely will be included into the next update.
done for main french calendar (till 2028) 
Pardon, what is done? I mean, I don’t see any pull requests into the repository, nor anything in the email.