The question seems to be sufficiently on-topic, but the wording is not ideal. You should try to write it so there isn't any question about what you're asking. We often have to guess at the intended question based on the title: your title suggests the question is about historical development of languages, but the body asks about how many languages were known to exist at a certain time. The title and body should ask the same question. You include the text "Aramaic etc. -> Hebrew, Arabic" which we can't interpret: I would guess that you're claiming that "Aramaic etc." developed into Hebrew and Arabic, which is false and meaningless given that we don't know what "etc'" refers to. Anyhow, that final bit of text is a distraction.
The core of the question seems to be simply "Is it possible to say how many languages where known at that time". There are two obstacles to answering such a question: (1) known by whom? and (2) at what time. First, you need to refer not to a biblical story, but to a concrete time period -- such as "during the reign of Darius" (okay, too late) or "around 2,000 BC". Second, you need to contextualize the knowers – I think the answer w.r.t. the Germanic tribes is "a couple", and the answer w.r.t. the average educated Mesopotamian resident is, errh, dozens, and the answer w.r.t. the handful of people who represent the pinnacle of Mesopotamian science might be a hundred.
There is a third problem with the question, which might suggest that the question is not suited for this site, but that is not my intention. The problem is that the question almost certainly would only generate speculative opinions and not true facts. Or, it would generate the 1-word answer "no". I basically made up my numbers, any the next guy can make up different numbers. The problem is that the question reads like a request to know how many languages people were aware of at a certain time, and we have next to no basis for answering that question. The bulk of your question seems to be about that; yet what you as is "Is it possible to say...", which is really about research methodology.
So I would think carefully about whether you are asking a methodological question, or a historical-factual question (about actual awareness of languages), and then make the question fit your intent.