Description
(Filing as a separate issue as per #53 (comment) )
As with HTML's lang/xml:lang properties, it would be useful to indicate the content language of a particular field in a standard manner. This might be used for proper font display (as in CJK languages) or for selectively showing content to users based on their locale.
I think a name "contentLang" for the property would avoid confusion at (falsely) thinking that this was necessarily indicating the language of the "title" or "description" itself.
Although it is probably not a feature that would be used for validation (since looking at code points might not be reliable or valid such such detection), contentLang does describe the data, placing constraints on how it is to be understood which brings it more into the world of schemas (unlike i18n of the schema itself).
Note that JSON-LD would not solve this unless one uses JSON-LD in the instance documents (which would prevent the benefit of having such a pseudo-constraint at the schema level).