What
The schema Claude Code uses when publishing or updating an Artifact page (a shareable rendered page, like a small app or document) no longer includes a lang field. That field used to hold a standard language tag (like "ja" for Japanese or "pt-BR" for Brazilian Portuguese) which became the page's <html lang> attribute, and its description text about matching content language was removed along with it.
Why
Anyone building or inspecting artifact publish requests will no longer see or be able to set a lang value; the tool's schema is simpler but pages published through it no longer get an explicit language tag set this way.