¡Por si las moscas!
Anyone translator living in his or her source-language country needs to watch out for source-language interference. Similarly, an author who writes in one language but lives in a country that speaks a different language needs to be wary of interference from the host country’s language.
Today, Google recommended an article to me in which I noticed foreign-language interference almost from the beginning. See if you can spot it too in this article about the level of English in Spain, then click on “Continue reading” to reveal the answers.