Is it necessary that the sources always be in the English language? Under what conditions is it valid to answer questions from non-English sources?
It is a question that I have for a long time, I have always assumed that it is valid, for example if it is a very precise data of a very unusual investigation, but on the other hand somehow I have always forced myself to find the materials in English language. We should specify certain situations because I think I have not been able to be as specific as I would like in some answers.
So: Should the questioners be asked if they want a data from a source in another language? Should I always deal with a translation in addition to the response? In the latter case should I translate the entire document?