I don't agree so much with this approach. First of all because of DForck42's argument, which is the same reason why the
action tag is discouraged on a question about Mission Impossible.
And furthermore we would have to use this on all questions, tagging "non-foreign language movies" (from the point of view of this question) as
english. The reason this site's language is English is not because it is mainly about English language movies or because the community is centered around English native speakers, but because the community is international and multilingual (a case for which English has established itself as lingua franca). English is the language of this site, not of the topic discussed on this site. Therefore English language movies theoretically don't have a special position among the movies discussed on this site (they practically have, because those are the ones most people have seen and can discuss about).
And even more than that, the language in which a movie was produced doesn't say much about the movie at all (if it can even be decided clearly, see The Good, The Bad and The Ugly). What you may be after are the countries or, much more important, the cultures which the movies were produced in. But this cannot be decided that easily either. And who then decides that Korean movies are more worth to mention their origin than Hollywood movies or other U.S. movies or other English movies or movies produced in Romania, France, Germany or Nigeria?
On the bottom line, this policy is just too subjective and segregating if enforced for some movies only and too hard to do and utterly irrelevant if enforced for all movies.