I sometimes see questions in a foreign language, translated below. Is it acceptable to answer the question in both English and the OP's language(if I speak it) to make the process simpler for the OP? Or does that encourage improper use of foreign languages here?
As far as other languages we have extended discussions about it already in meta, the key points are:
Users that post questions in other languages normally do not participate on the site or will even bother to come back and check the replies, specially if they are in English. You can see a lot of questions that even with translation under them will be closed as too localized because the information on them is not enough and the OP will not reply to comments.
Its a shame, but that is the way it is. Localization of SE sites using other langauges is discussed with many for and against points, nothing we can do more for now.