Question: What language(s) do Simulacrum know before Limited Wish is cast?
Answer: it knows whatever language the Wizard commands it in verbally, written, or physically.
The limitation that the simulacrum cannot be commanded telepathically is meant so that a player cannot cheat and have the simulacrum speak knowledge that is being telepathically transmitted to it by the caster to appear more authentic. In its unmodified state, it acts more like a zombie, and obeys only the casting wizard. It is supposed to be easily identified as a decoy unless you were to cast resurrect and limited wish on it.
So, the possibility of a telepathic link was removed. However, it doesn't just understand the wizard's speech, it can also understand written text and other bodily signals, as long as it originated from the wizard.
It is an Illusion/Phantasm and as such is manipulated by the wizard's magic. Magic is fun in D&D since it oftentimes overlooks logic. If it was logical it would be a gnome's construct. So the language it knows is the wizard's own, whether it be Draconian, Common, or Sign language. Crazy cool that a simulacrum could understand and read Draconian and yet be duller than my 20-year-old kitchen knives.
Again, I must stress that this impedance of telepathic link was created to prevent a simulacrum from appearing more authentic than it is in its base form. Not necessarily to create confusion as to its intelligence modifier.
Here's the official text from 2e I am referencing:
[...] there are areas of knowledge that the duplicate does not have, and a detect magic spell will instantly reveal it as a simulacrum, as will a true seeing spell. At all times the simulacrum remains under the absolute command of the wizard who created it. No special telepathic link exists, so command must be exercised in some other manner. The spell creates the form of the creature, but it is only a zombie-like creation.