This is one of those books that you appreciate on an abstract, formal level more than anything else - which isn't to say only analytically, because really, the ultimate enjoyment is in just kind of immersing yourself and letting it wash over you. But it's not a plot driven story. Though there IS a kind of plot, in that various phrases or fragments recur with various modifications and start to form some kind of story - we learn that the narrator is a translator, that she was born in France but sent to live in Germany, that she has some vague romantic entanglements, etc - that's not really the point. It's more of an experiment in multilingual mood, I guess. Which you may find interesting (as I did) or horribly pretentious and frustrating.
So here's my plug for why it's not just self-indulgent - unlike Gloria Anzaldua's Borderlands, which also shifts languages, but out of a more self-serving desire to express in the most self-authentically possible way, reader be damned, this seems like more of an attempt to consider what the differences between languages really do. Often, the same word will be recited in 5 different languages, as if to see if it really is the same. There are moments that, to me, evoked the experience of being in a foreign country and encountering things in a different language, where even if you know what it means, it's still just different somehow. Being a person who has travelled a lot and had the somewhat alienating experience of not knowing the language at all, or of knowing it but still feeling rather alien, there was something really familiar to me about this book, and I kind of loved it. But it's definitely not for everyone.