Should I feel guilty...

I have had bits of German dialogue in two of my novelettes and have French and Latin dialogue in an upcoming novel. Never had any complaints either. As long as it's clear what's going on, I don't think it's necessary to translate them (though you could offer a translation on your website or an appendix of the actual e-book).

BTW, if you use dialogue or quotes in another language in your book, please make sure to have it translated or checked by someone who is fluent in the language in question, preferably a native speaker. Cause mangled foreign language passages can be annoying at best or unintentionally hilarious at worst, such as the Nazi general in an old Wolverine comic who ordered his soldiers to drop their excrements (the actual term was ruder, but the profanity filter will eat it) rather than shoot. Okay, so Wolverine's sense of smell is supersenstive, but I still don't think that was what the general had in mind. Or - Marvel comics were really bad about mangling languages - Nightcrawler addressing Emma Frost as "undershirt" (which totally baffled me, because though Emma Frost's corset was very noticeable, Nightcrawler never struck me as a misogynist) rather than "darling".

And for a reverse snafu, how about the German dubbing of Downton Abbey, wherein the characters kept addressing Maggie Smith's character as the Countess of Dowager rather than the Dowager Countess of Grantham, because whoever did the translation did not know what a dowager was.

This is not directed at JR BTW, because I know she does proper research, but to anyone who wants to include foreign language bits in their fiction.