feat(web): i18n with react-i18next (sv/en)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/src/i18n/en.json

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+{
+  "app": { "name": "Collection" },
+  "nav": { "objects": "Objects", "vocabularies": "Vocabularies", "authorities": "Authorities", "fields": "Fields", "search": "Search", "soon": "Coming soon" },
+  "auth": { "email": "Email", "password": "Password", "signIn": "Sign in", "signOut": "Sign out", "invalid": "Invalid email or password", "networkError": "Could not reach the server" },
+  "objects": { "title": "Objects", "empty": "No objects yet", "loadError": "Could not load objects", "selectPrompt": "Select an object to view its details", "notFound": "Object not found", "prev": "Previous", "next": "Next", "of": "of" },
+  "fieldsLabels": { "objectNumber": "Object number", "objectName": "Name", "count": "Number of objects", "briefDescription": "Brief description", "currentLocation": "Current location", "currentOwner": "Current owner", "recorder": "Recorder", "recordingDate": "Recording date", "visibility": "Visibility", "flexible": "Catalogue fields" },
+  "visibility": { "draft": "Draft", "internal": "Internal", "public": "Public" }
+}

web/src/i18n/i18n.test.tsx

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+import { expect, test, beforeEach } from "vitest";
+import { render, screen, act } from "@testing-library/react";
+import { useTranslation } from "react-i18next";
+import i18n from "./index";
+import { useLocale } from "./use-locale";
+
+beforeEach(async () => {
+  await i18n.changeLanguage("en");
+});
+
+function Probe() {
+  const { t } = useTranslation();
+  const { setLocale } = useLocale();
+  return (
+    <div>
+      <span data-testid="title">{t("objects.title")}</span>
+      <button onClick={() => setLocale("sv")}>sv</button>
+    </div>
+  );
+}
+
+test("switches language at runtime", async () => {
+  render(<Probe />);
+  expect(screen.getByTestId("title")).toHaveTextContent("Objects");
+  await act(async () => {
+    screen.getByRole("button", { name: "sv" }).click();
+  });
+  expect(screen.getByTestId("title")).toHaveTextContent("Föremål");
+});

web/src/i18n/index.ts

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+import i18n from "i18next";
+import { initReactI18next } from "react-i18next";
+import en from "./en.json";
+import sv from "./sv.json";
+
+export const LOCALE_KEY = "locale";
+const stored =
+  typeof localStorage !== "undefined" ? localStorage.getItem(LOCALE_KEY) : null;
+const fallback = "en";
+
+void i18n.use(initReactI18next).init({
+  resources: { en: { translation: en }, sv: { translation: sv } },
+  lng: stored ?? fallback,
+  fallbackLng: fallback,
+  interpolation: { escapeValue: false },
+});
+
+export default i18n;

web/src/i18n/sv.json

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+{
+  "app": { "name": "Samling" },
+  "nav": { "objects": "Föremål", "vocabularies": "Vokabulär", "authorities": "Auktoriteter", "fields": "Fält", "search": "Sök", "soon": "Kommer snart" },
+  "auth": { "email": "E-post", "password": "Lösenord", "signIn": "Logga in", "signOut": "Logga ut", "invalid": "Fel e-post eller lösenord", "networkError": "Kunde inte nå servern" },
+  "objects": { "title": "Föremål", "empty": "Inga föremål ännu", "loadError": "Kunde inte ladda föremål", "selectPrompt": "Välj ett föremål för att se detaljer", "notFound": "Föremålet hittades inte", "prev": "Föregående", "next": "Nästa", "of": "av" },
+  "fieldsLabels": { "objectNumber": "Föremålsnummer", "objectName": "Namn", "count": "Antal föremål", "briefDescription": "Kort beskrivning", "currentLocation": "Nuvarande plats", "currentOwner": "Nuvarande ägare", "recorder": "Registrerad av", "recordingDate": "Registreringsdatum", "visibility": "Synlighet", "flexible": "Katalogfält" },
+  "visibility": { "draft": "Utkast", "internal": "Intern", "public": "Publik" }
+}

web/src/i18n/use-locale.ts

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+import { useTranslation } from "react-i18next";
+import i18n, { LOCALE_KEY } from "./index";
+
+export function useLocale() {
+  const { i18n: instance } = useTranslation();
+
+  const setLocale = (lng: "en" | "sv") => {
+    localStorage.setItem(LOCALE_KEY, lng);
+    void i18n.changeLanguage(lng);
+  };
+
+  return { locale: instance.language, setLocale };
+}