He reportedly based Khuzdûl (the secret language of the Dwarves) on Hebrew. So he for sure had a basic understanding of Semitic languages. If you study a language - even briefly - usually you have some example text fragments to "learn on". From there it is not far to check the rest of a text in the library, if one want to know the context.In a couple of his letters he does mention his admiration for Jews but my impression is that he didn’t know many. The Jewish linguists of his time would not have been Germanic philologists (let along Anglo Saxon) - more Slavic or Semitic languages. So I don’t know what he knew about Jewish thinking.
Actually knowing of the mystic background of the divine light vessels makes me take the Silmarils more seriously as a literaly concept. Untill now I kind of dismissed them as "pretty jewels everybody is crazy about for no apparent reason". Now I kind off start to get the point of them a little better, thank you very much!