Multilingual (per-language trees) — Phase D3, optional

When the source has language trees (/fr/…, /en/… beside /de/…), add them as parallel content trees that REUSE the same block library — block structure is language-agnostic; only authored content and a few wiring pieces change. Proven on a ~90-pages-per-language add (≥5 per template).

• Author by mirroring the default-language archetype per type, in the target language. A target-language page is the default page's block composition with translated content at the localized path (e.g. /fr/…/<slug>). Dispatch author agents grouped by template-type, each given the default-language reference file to mirror — no new blocks.

• Language-route the chrome via per-language /nav + /footer documents. The stock header/footer blocks resolve their fragment path from nav/footer page metadata, falling back to /nav and /footer — no runtime code changes. Author content/fr/nav.html + content/fr/footer.html (and en/…) and set the metadata on each language tree's pages (or, cleaner, add the path-prefix fallback once in the header/footer BLOCK's decorate(): derive /${lang}/nav from window.location.pathname when no metadata is set). The documents carry translated labels, links localized to live same-language pages (else a source bounce), and a language switcher that targets each language's home — don't try to compute per-page cross-language equivalents. Per-language chrome documents are published content: they belong on each language's publish roster.

• Per-language indexes in helix-query.yaml: clone each index with a language-scoped include glob + a language-prefixed target, and fix the selectors that encode language — a facet selector like a[href*="/specialites-medicales/"] (FR) / a[href*="/specialities/"] (EN) is not the default-language a[href*="/fachgebiete/"]. Same metadata contract per type.

• Path-safety is per-language too. The leading/trailing--, --, _, and uppercase normalization (delivery-gates Gate 3) applies to every language tree — record slugs in particular recur with a leading hyphen across languages.

• The per-language indexes are empty until the pages are published under the synced config — same republish that propagates a head.html change (see operational-learnings).