Zone 8 — document lang: each adapter's page shell (html, astro, nuxt, next, eleventy, sveltekit) sets lang={config.locale ?? 'en'}. Audit all six adapters (SPEC-030, SPEC-058); add a shared helper if it reduces drift.
Number / duration / currency formatting: the duration transform consults Intl.DurationFormat (or a polyfill) for locale output; budget amounts use Intl.NumberFormat(config.locale); currency uses Intl.NumberFormat style: 'currency', replacing the manual BUDGET_CURRENCY_SYMBOLS lookup.
Tests: a non-English locale sets lang on every adapter's shell and formats a duration/number/currency per locale.

Acceptance Criteria

All six adapter page shells emit lang from config.locale, defaulting to en.
Duration, number, and currency formatting are locale-aware via Intl.
Zero-config (en) output is unchanged.

Blocked by