Bonjour Alexandra,
It's great that you are planning to visit
Glendalough! The monastic site and the entire valley are definitely worth the trip to the
Wicklow Mountains. Will you be staying in Dublin the rest of the time?
While I don't know French tour operators organizing this tour, I'd suggest you reach out to French-speaking tour guides in the Dublin or Wicklow area. These can be found on the
Irish Tour Guides website.
Otherwise, it's also possible to take
St. Kevin's Bus and see the valley yourself.
A bientôt,
Antoine