Gene,
The French word “entaillage” has several different meanings, but, in this case it refers to the notching on the back of the action, that meets the wood on the gun on the left. The boxlock on the right is straight up and down in this area, and less of a challenge to fit the wood to the back of the action. It will be cheaper, typically. Other than that detail, both actions are remarkably similar. More decoration on the gun on the left, but, the nuts and bolts operation is pretty much identical.

French gun making terms are a language of their own, and truly fluent French speakers/writers can become hopelessly lost in them.

Best,
Ted