Shalamar, I know I posted about this before, but a while ago I tried a thriller/adventure novel, based around a big conspiracy to continue Nazi experiments into unlimited energy, or time travel, or something of the like. Unsurprisingly, quite a few of the characters in the book were German, so there was a lot of very basic German dialogue thrown in. The number of errors was phenomenal - and really, really basic errors, too. It was so distracting that I gave up on the book.
I do understand that authors sometimes want to write dialogue in a foreign language, but for goodness' sake, get a native speaker, or even a student of the language, to check it before it goes into print!