The only way to use a different language is to write about foreign languages as if they are a topic.
I wrote a Hub about the differences between Spain and Holland, pointing out the way they flirt and how they compliment men and women in general.
I use Spanish to explain these differences and translate those few sentences to English. I don't overdo the Spanish but in this Hub it adds to the whole subject.
Writing a complete Hub in Spanish, Dutch or French would be a dream to me but we're not yet there....I'd love to see that day coming though!