I have made it a sort of informal rule that whenever an opportunity arises to see an Icelandic film, I seize it. Especially if the description is somewhat bizarre. Because in my experience, Icelandic films are fantastic and weird and actually, they are just like their descriptions, it's just that they are so off-beat and quirky that they can't really be described, except it extremely basic plot points which do not do justice to the whole. Queen of Montreuil is indeed about a French woman who returns to Montreuil to grieve over her husband's death, and then somewhat randomly an Icelandic woman and her son arrive, and also a sea lion. It won't make any more sense to add that the Icelandic woman is returning from Jamaica, where another son of hers lives, or that she befriends a construction worker. Nothing is really going to give you any sense of what this movie is like, except to say that it's funny and sweet and just overall great. The plot, inasmuch as there is one, is subtle and understated, allowing information to emerge gradually, except when its fantastically improbable in a delightfully absurd sort of way.
Just go see it, if you can.