What do the levels stand for in French Air Traffic Service Levels?
This NOTAM concerns the fire and rescue level not the ATS operating hours.

You can find the description of the fire and rescue levels here.

The reference of the ATS hours is to say the level is raised during the opening hours of the ATS.

The ATS opening hours are available on the Visual Access Chart from the SIA. (French service for aeronautical information)

Where you have on last page:


  SUMMER 0700 - 1800


Finally for the language, you have to speak French when the ATS is closed.