What is DA BEP LECH underneath TOUTES DIRECTION?
Google suggests it's a (tiny) brewery. I assume this sign would be in the vicinity of Morlaix (Bretagne) where this brewery is apparently located. While I've passed through Morlaix a couple of times (long ago), I'm not familiar with the brewery or its produce.
Do you know why the other 2 exits are not labelled with where they lead.
Generally they're exits of minor importance. It's for instance common for exits to a gas station or DIY store etc. to not be labeled. The labels in italics (such as the one you referred to above) are generally private names instead of generally accepted geographical indications; i.e. names of specific stores/shops/businesses, industrial zones, specifications to regular geographic names etc.
Is it that they literally lead to nowhere
Yes, you will fall off the planet's disc if you take any of these exits. You will then tumble past the four major elephants and may eventually smash onto the turtle's shield, unless your vehicle had sufficient escape velocity to clear it, in which case you may catch a glimpse of the turtle's belly once you've passed it.
and that by turning on the third exit for all directions you will find further directions on the next exit?
The sign does indeed mark the entry point of the geographical equivalent of the '
Droste effect', where taking the appropriate exit will get you stuck into an infinite loop of identical roundabouts that succeed each other. The existence of such anomalies is one of the causes of the trend of depopulation of the French countryside.
To pre-empt the question you have not yet asked, likely because you so far have overlooked it: the break in the circle of the roundabout signifies a further trait of French road design and signage, where each roundabout is in fact a single-story element of a spiral with N cycles, with N = 0...∞, and N furthermore not being limited to integers. For instance, take this sign here:
This signifies a roundabout that is the section of a 3-dimensional spiral, with the number of cycles being 30m, with 'm' standing for 'milli'. Hence, there are only 30 milli-cycles and thus, the roundabout only covers 38880 arcseconds. Since it is in effect a real roundabout (i.e. you do find yourself facing the same direction as you traverse a full cycle), you can deduce from this that in constructing French roads, it is common that the fabric of spacetime is subtly twisted or (as is the case here) bent quite significantly in order to allow for the unique and inventive arrangements of French logistics. It may also be more obvious to you now why France is the place where nuclear fusion has been in developed for decades, high-speed rail originates and supersonic passenger airflight was once upon a time fairly common - it is in the nature of French transportation to be flexible when it comes to Newton's suggestions of how we (and indeed, all physical bodies) should relate to each other.
Edit to correct a bleedingly obvious math error - duh!