RE: [Techniques] Draft General Technique for GL 3.1 L2 SC3

 >3. I am not suggesting to modify the SC in a way that every foreign word,
   >included or not included in dictionaries, should be marked in the code with
   >the appropriate lang code. I am rather suggesting that _no passage or
   >phrase_ written in a foreign language should be marked in the code. When
   >possible, authors should resolve potential ambiguities in the content
   >modifying the wording or linking some words to glossaries and dictionaries.
   >
   >GV  ok  This is one that we have been thinking about a lot.  No resolution
   >yet. 
  
http://www.w3.org/TR/i18n-html-tech-lang/

I suggest also to read this... Every word not in the declared primary language(s) must Be marked. It's rigjt reading will be an user agent issue, but the markup is a web developer or - in these times where cms are ruling - web content editor.