What is the origin of the combination of these two meaning types in a single word, which we seem to find in some related languages?
Type A: a certain teacher / ein bestimmter Lehrer / un certain professeur
Type B: a certain death / bestimmte Vorstellungen / une mort certaine
The answer I am looking for might look like: "It originates with the Latin expression ___, which had Type B meaning first and later Type A. The expression made its way into French and, through it, to English and influenced a similar development for the German word."
You don't need to read what follows to answer the question. I will only try to motivate the question a little.
Type A limits a larger set to a smaller. By saying, for example, "Certain species of the forest adapted to the change," we signal that we are talking about a limited subset of the forest species though at this time we won't go into the selection criteria.
Likewise, in saying, "A certain popular teacher thought he could make more money by opening his own school," we signal that we have in mind a particular member of the set of popular teachers though we won't be giving out any names.
We may say that type A certain is not a characterization.
Type B is a characterization. If we say, "Death was swift and certain," certain is on a par with swift.
Alternatively we may say that type B certain is also different from swift by analyzing the sentence to death having the attribute of swiftness and nobody having any doubt of its coming.
Anyway, only type A usage of certain can elicit the question, "Which?" Imagine this conversation: "Charles is facing a certain death." "Which? By hanging? The guillotine? I'm dying to know." "No, I mean they are sure to kill him."
If all the languages you know have this combination of types A and B in a single word, the connection between the two may seem entirely natural and even inevitable, but I can tell you that it is at least not inevitable.
I'd be surprised if the combination occurred independently in many languages. Thanks.