Tolkien was almost certainly familiar with Sumerian myth. I believe he alludes to it in one of his letters. (I can track this down if you want; it's just late and I'm lazy ...)
I hesitate to attribute direct inspiration from myths in all but the most blatant instances (like the connection between the Finnish Kullervo and Turin), mostly written when JRRT was very young. I think, instead, that he read so deeply of myth and folklore and internalized the motifs and archetypes that made those stories tick as myths and folktales, and he applied them naturally in his own work, creating the sense of the mythic without resorting to direct imitation. This is what I've found in my research on his cosmogony: He relies more on motifs and archetypes than a direct patterning of his work after an existing myth.
In light of Himring's comment, I see that here too: the interweaving of multiple mythic/folkloric elements into the story of Luthien. It'd be interesting to survey the myths he was most familiar with to see what elements they share in common with the Luthien and Beren story.
no subject
I hesitate to attribute direct inspiration from myths in all but the most blatant instances (like the connection between the Finnish Kullervo and Turin), mostly written when JRRT was very young. I think, instead, that he read so deeply of myth and folklore and internalized the motifs and archetypes that made those stories tick as myths and folktales, and he applied them naturally in his own work, creating the sense of the mythic without resorting to direct imitation. This is what I've found in my research on his cosmogony: He relies more on motifs and archetypes than a direct patterning of his work after an existing myth.
In light of Himring's comment, I see that here too: the interweaving of multiple mythic/folkloric elements into the story of Luthien. It'd be interesting to survey the myths he was most familiar with to see what elements they share in common with the Luthien and Beren story.