I don't speak French. I don't speak German. I don't speak any language other than English (oh, and the international language of love, of course). So when a novelist, usually a contemporary literary novelist, presents me with big chunks of text in a foreign language I simply haven't got a fucking clue what they are talking about. They have therefore lost me. Game over. Finis. Kaputt.
I do appreciate that a lack of a foreign tongue is my loss. I dearly wish I could speak another language but like driving a car, the periodic table and musical prowess, it is something that is beyond me. My brain just doesn't seem to work that way.
And because of this I get miffed when I come across lines, paragraphs, whole sequences sometimes, in another language. The odd word here and there, especially in dialogue, I can live with and can usually guess at a meaning. But long show-offy chunks are another pet book hate.