Add i18n support: per-locale catalogs, URL-driven locale, translated core and examples

src/i18n/view-locals.ts

@@ -0,0 +1,48 @@
+// The i18n block every rendered view receives. EJS passes a template's locals down into its
+// includes, so injecting this at the top level is what lets any partial — core or plugin — call
+// `t(...)` and read `locale` without its caller threading them through.
+
+import { DEFAULT_LOCALE } from "./catalog.ts";
+import { ENGLISH } from "./english.ts";
+import type { RequestContext } from "../http/context.ts";
+import { localeHref, localeLabel, textDirection } from "./locale.ts";
+import type { Translate } from "./translate.ts";
+
+export interface LocaleChoice {
+  current: boolean;
+  href: string; // this same page in that locale
+  label: string; // the locale named in its own language
+  tag: string;
+}
+
+export interface I18nLocals {
+  dir: "ltr" | "rtl";
+  locale: string;
+  localeHref: (href: string) => string;
+  localeSwitch: LocaleChoice[];
+  locales: string[];
+  t: Translate;
+}
+
+// For a render with no request behind it — a partial exercised directly, a one-off render: English,
+// left-to-right, no language picker.
+export const ENGLISH_LOCALS: I18nLocals = {
+  dir: "ltr",
+  locale: DEFAULT_LOCALE,
+  localeHref: (href) => href,
+  localeSwitch: [],
+  locales: [DEFAULT_LOCALE],
+  t: ENGLISH,
+};
+
+export function i18nLocals(ctx: RequestContext): I18nLocals {
+  const here = `${ctx.url.pathname}${ctx.url.search}`;
+  return {
+    dir: textDirection(ctx.locale),
+    locale: ctx.locale,
+    localeHref: (href) => ctx.localeHref(href),
+    localeSwitch: ctx.locales.map((tag) => ({ current: tag === ctx.locale, href: localeHref(here, tag), label: localeLabel(tag), tag })),
+    locales: ctx.locales,
+    t: ctx.t,
+  };
+}