I think the natural solution is to allow Mainspace and Wikipedia-space. Policies, guidelines and essays are often useful for translation. They may have little impact on article translation metrics, but can have a large impact on the Wikipedias. This would not be arbitrary because it is supported by community and anyone likely to translate a Wikipedia-space page is not going to do this by accident. As I see it the call to block template, module, talk, etc. is mainly to prevent accidental translations that are useless or where the tool is not useful, not to restrict vandalism, because that is just as likely to occur through translations of Mainspace articles.