I can't speak to a social or political historical perspective on this, but from a literary historical perspective, it would stand to reason that a group organized around the Torah would prize literacy.

YHWH, as depicted in the Hebrew Bible, is a god of laws, contracts and words above all else. The first creative act in Genesis, "Fiat lux!", is an utterance.

The story of the Torah (as much as it has a single story) is an elaboration of a covenant between the entity that created the universe and a particular tribe of human beings - for the faithful, being able to parse every detail of that agreement is part of the deal. For instance, Jacob - who becomes Israel, the forefather of the Israelites - gets his status by taking an agreement literally.

In Deuteronomy 30, YHWH spells it out: "The word is very near you; it is in your mouth and in your heart so you may obey it."

YHWH bans likenesses but is said to be physically present in the place where his word, the commandments transcribed by Moses, are kept.

So the word - literacy, contractual understanding, correct interpretation - is probably the most fundamental theme of the entire Hebrew Bible.

You can get more background on this from The Jewish Encyclopedia's entry on memra, or "logos," which among other things lists some of the instances in which YHWH is metonymically referred to as "The Word," or sends his word out as if it was an angel.

This may be more an expression of the cultural value of literacy than a cause, but it's definitely a major component of Judaism.

Not entirely true. The Jewish prayer service includes a repetition of the Amida (silent prayer) by the cantor. This was intended to allow any and all attendees to answer 'amen' and fulfil their prayer obligations despite not knowing how to read. There are other such laws (all of rabbinic origin) designed with that purpose.

Source: Shulchan Aruch, OC 124:1

Would they only learn Hebrew? Or would they also learn the local language?