The problem is that sometimes the posters just don't know and other times they just forget to mention.
Of course many ID questions could be made a lot easier and better if each and every asker would mention each and every detail he remembers about and this is in turn encouraged for identify questions (and more often than not enquired by further comments if not mentioned). But unfortunately it is entirely up to the asker to write a proper question and there is IMHO no proper automatic way to make the asker write down everything he remembers other than asking guidelines.
Yet I also think that most often when people are explicitly searching for a "foreign" movie (and know this), they also mention it, since English-language movies still have a special meaning to most posters (be it by cultural background, prevalence in cinema/TV, site language, ...). So I think the country of origin is less of a problem than other details of ID-questions (or their general quality for that matter) and if not mentioned, one can often safely assume an at least English-language movie (yet asking in a comment if not mentioned at all would be the safest bet).
But I agree that it should at least be added into the "identify-guidelines" in the help section and would encourage the moderator(s) to do so.
In the end this comes down to the general requirement to write "good questions", which is unfortunately not clearly definable nor enforcable other than by further comments and refinements of the question (as is IMHO especially a problem with ID-questions as those seem to appeal to unregistered one-time-and-never-again visitors more than any other question type, but this might be just my subjective impression ;-)).