It is difficult to say whether or not "Fertigungstiefe" is a word that has a wide-spread equivalent in English.

A brief look into the Internet showed that of the 71 hits for "vertical range of manufacture", nearly all of them were from German sites, raising the suspicion that it is a term some translators have used out of necessity.

An alternative could be "the portion of in-house production (make or buy)" but it is almost a definition. Perhaps there is no way around using some sort of description.

Another alternative term is "manufacturing penetration." But this is used not just for a single company but also for a region's level of industrial activity. As a "Fachbegriff", it would require more explanation to make its meaning clear.

There is however the traditional distinction between the two terms "manufacturing" (production from (semi-) raw materials) and "assembly" (putting parts together).

We manufacture parts for the automobile industry. (largest "Fertigungstiefe")
We produce parts for the automobile industry. (unclear "Fertigungstiefe")
We assemble parts for the automobilie industry. (lowest "Fertigungstiefe")

These terms, however, would not be applicable to the service economy, i.e. they are only for the industrial sector. "Lean production" and "streamlined production" would describe a particular state with regard to "Fertigungstiefe".