@youneed/server-middleware-accept-language

Server-driven content negotiation on the Accept-Language header for @youneed/server. Parses the header's weighted language tags, picks the best match from the locales you actually ship, stashes it on ctx.state.locale, and advertises the choice with Content-Language (+ Vary: Accept-Language).

import { Application, Response } from "@youneed/server";
import { acceptLanguage } from "@youneed/server-middleware-accept-language";
import { i18n } from "./i18n.ts"; // an @youneed/i18n instance

Application()
  .use(acceptLanguage({ supported: ["en", "de", "fr"], default: "en", i18n }))
  .get("/", (ctx) => Response.text(`locale: ${ctx.state.locale}`))
  .listen(3000, () => {});

Matching is case-insensitive and language-aware: de-AT matches supported de (primary-subtag fallback), q=0 rejects a tag, and * (when nothing else matched) takes the highest-priority supported locale. Pass an i18n translator to set its active locale per request.

Also exports the pure helpers parseAcceptLanguage(header) and negotiateLanguage(header, supported) for use outside the middleware.

| option | default | meaning | | --- | --- | --- | | supported | — (required) | locales you ship, most-preferred first | | default | supported[0] | fallback when the header is absent / matches nothing | | stateKey | "locale" | key under ctx.state for the negotiated locale | | i18n | — | translator whose setLocale is called per request | | contentLanguage | true | emit the Content-Language response header | | vary | true | append Accept-Language to Vary |