It’s quite common these days to use foreign words or phrases to make your speech or writing sound a bit more interesting, cosmopolitan or even learned. It should be done with caution, though, as this article in the Guardian demonstrates. There are just so many opportunities for error and embarrassment; you might find you’ve completely confused the issue with the reference, accidentally allied yourself or your writing with something inappropriate or offensive, or just left those fluent in the language you borrowed from in fits of laughter.
The same can happen the other way around, of course, dropping English words into conversation in another language. Big companies have made some famous mistakes in this area over the years, my favourite probably being the Rolls Royce model that had to be renamed in some countries because it’s English name meant something very different to ‘high quality’, ‘luxury’ and all the other typical Rolls Royce values!