I think it matters to recognize that what matters with this Divine "tablet" is its knowledge function, not its physical form which seem to be symbolic or subjective as I'll just explain.
The language indeed seems redundant because what you have in al-Lahw al-Mahfuz is Divine supreme knowledge not written words as words are human conventions after all and have no metaphysical significance. Should one invoke traditions that claim a particular language for angels or paradise as a hint, well, these traditions are weak in isnad and highly suspect of nationalistic forgeries.
And there's a more subtle observation here too. People often tend to associate knowledge with words but they are different. Words signify rather than constitute knowledge. That's why you can have multiple languages referring to the same meaning by different words.
With that said, it is very likely the case that knowledge in this Divine tablet will be rendered in the language of the individual person who accesses it. So if an Arab can access the tablet the knowledge will appear to his mind in Arabic. If a Persian accesses it, the knowledge appears to it in Persian. This is consistent with the fact that we have had prophets from different languages and dialects receiving various forms of revelation in their own language. Even the actual mechanism of it I believe can be laid out. Because in our mind all meanings are associated with words, then if some of those meanings are inspired in us from a higher source they will automatically and by consequence also invoke the words associated with them in our minds, just as the vice versa happens to us every day in this life: we hear only the sounds of words but immediately recognize the meanings associated in our minds with those words, because the sensual perception of the physical words automatically evoke the meanings.
Or it can be the case that the knowledge doesn't expresses itself in words or meanings at all which would be the case if the knowledge is presented in visual theatrical forms which can be the case in case of knowledge about events or actions. In such case, the said event or action is played out in visual forms and scenes upon encounter with it in the tablet. So the person observes the event and then describes it in his own language. So there's no mediation of language or even meanings here. A physical scene observed during the encounter with the tablet is only reported.
So there are various ways the knowledge can appear to the person.
A useful comparison here is Akashic records which seem to be the New Age equivalent of Al-Lawh al-Mahfuz. People claiming encounter with the Akashic records usually report encounter with an old massive library in which knowledge of the past and future events and facts are kept. Knowledge revelation from this supernatural library usually appears to the people as a book moving out of the shelves to them with animated stories opening before them and showing them an event or fact from past or future or some unknown contemporary place.
In Islamic traditions though, there's a talk of tablet and book as we know. Considering the rendering mechanisms I explained above, I tend to believe physical symbols associated with Divine knowledge tend to be subjective and cultural. That's because, in general, spiritual realities tend to appear to the people in forms they are most familiar or convenient to them. So it is just as possible to encounter a book, a tablet, or a library when encountering Divine knowledge, just as it is likely that you encounter Arabic or Persian letters or voices when you encounter it. This is consistent with Islamic traditions that say Allah Himself appears in different forms to the people in the Afterlife. But being a general metaphysical principle, this is not just true for Allah; it is true for all spiritual beings. Angels also appear in various forms depending, on the one hand, on the meaning of their revelation and, on the other, the subjective conditions of the person encountering them.