According to Activity Streams specs:
Activity Streams 2.0 publishers SHOULD explicitly mark the language of natural language properties if they are known, using either map properties or a default language tag.
The special language tag "und" can be used within the object form to explicitly identify a value whose language is unknown or undetermined.
It seems that Hubzilla don't follow the spec and don't add any language tag.
Please add those tags, to allow the Fediverse to become truly internationalized.