Openfire does not add xml:lang attribute to stanzas when routing/delivering

Openfire disregards this sentence from RFC 6120 § 4.7.4. xml:lang:

If the initiating entity does not include the ‘xml:lang’ attribute in any such stanza, the receiving entity SHOULD add the ‘xml:lang’ attribute to the stanza when routing it to a remote server or delivering it to a connected client, where the value of the attribute MUST be the identifier for the language preferred by the initiating entity (even if the receiving entity does not support that language for human-readable XML character data it generates and sends to the initiating entity, such as in stream or stanza errors).

That is, if a French client sends a stanza to a German client without the xml:lang attribute (because it is implicitly French), the German client thinks the stanza is in German, although it is French, due to the lack of the xml:lang (it assumes it is the same language as it’s own stream, German).

I’ve created [OF-2045] - Ignite Realtime Jira to track it.