An entry, title, abstract, etc., may be written in a language different from the default language of the feed. This is a very common case for synthetic feeds (e.g. a feed composed out of several feeds from different authors in different languages).
Add the following section to the specification:
3.1.3 "xml:lang" Attribute
Content constructs MAY have an "xml:lang" attribute, whose value indicates the default natural language of the content. When present, this attribute MUST be a registered language tag from RFC3066 or its successors; in addition, an empty string (xml:lang="") MAY be specified to indicate that there is no language information available.
Remove the following paragraph from section 2 of the specification:
Any element MAY have an xml:lang attribute whose content indicates the default natural language of the element's content. The content of this attribute element MUST be a registered language tag [RFC3066]. When determining element content's natural language, the first xml:lang attribute encountered in that element's ancestors MUST be used.
Has impact on what elements in an Atom feed one can specify language on.