If the movie's original title is in fact English, then that title should always be used, since it is the original title and fits to the language of this site. If it has an alternative English title in certain countries, then this should rather not be used, since this would be counter-intuitive as it is not the original title, even if it fits the language of the stie. Of course some people might not recognize it under the original, but so would it be with the alternative title for others and you cannot name each and every alternative title existing. One just has to make an objective compromise, and the original title is the best compromise possible, which is also what should be used for tags.
A much more interesting and difficult problem arises when the movie's original title is not in English (while it may still have an English title for English-speaking countries). In this case the two goals of matching the language of this site and refering to the movie by the most canonical name will deviate. I still tend to favor the site's language in this case, but I guess it may be a question by question (or movie by movie) decision. For some movies the alternative English title is very well-known, while others might not even have one. In some cases one can be lucky and they don't deviate that much (like here), or one chooses to name both titles (like here). But the point where a hard decision has to be made and where it also matters for the future structural integrity of the whole site is the tags. Since tags have quite a referential character it is important to find a consistent policy for those, of which I for myself am not completely sure at the moment.
But whatever title one uses in the question, in such ambiguous cases what always helps to quickly clear any confusion is a drect link to the corresponding Wikipedia article or IMDB entry (especially since IMDB can automatically show you the title in your language), a policy which I usually enforce in my own questions at least but would like to encourage in general.