Where is a suitably obvious machine-identifiable place (element or 
attribute) for the language code of the original document when the 
current document is a transcription of a translation? 

All our files have one or more profileDesc/langUsage/language/@id for 
the language[s] of the current document, which in the case of a 
transcription of a printed translation from (say) Spanish into English 
says just "en" because no Spanish words exist in the translation.
Should I [ab]use another language/@id or another attribute on the
existing language element[s] to identify the original source language,
and if so, how best to make it obvious that that is what it refers to?

Files also have a sourceDesc/biblStruct for the printed edition from 
which this transcription was made, and one or more much simpler bibl 
elements for the MSS used by the author of the printed edition. Is
the lang attribute on bibl* elements is intended to specify the language
of the bibl* element content, or can it be used to denote the language
the referenced document is written in?

///Peter