feat(i18n): add locale dictionaries and pilot surfaces

tests/unit/i18n/locales.test.ts

@@ -0,0 +1,48 @@
+import { describe, expect, it } from "vitest"
+
+import {
+  DEFAULT_LOCALE_ENV_VAR,
+  FALLBACK_LOCALE,
+  isLocale,
+  LOCALE_COOKIE_NAME,
+  resolveDefaultLocale,
+  resolveLocale,
+  SUPPORTED_LOCALES,
+} from "@/i18n/locales"
+
+describe("i18n locales", () => {
+  it("defines exactly English and Spanish with an env-configured default", () => {
+    expect(SUPPORTED_LOCALES).toEqual(["en", "es"])
+    expect(FALLBACK_LOCALE).toBe("en")
+    expect(DEFAULT_LOCALE_ENV_VAR).toBe("STOCK_MANAGER_DEFAULT_LOCALE")
+    expect(LOCALE_COOKIE_NAME).toBe("stock-manager-locale")
+  })
+
+  it("accepts only exact supported locale codes", () => {
+    expect(isLocale("en")).toBe(true)
+    expect(isLocale("es")).toBe(true)
+
+    for (const value of ["", "ES", "es-MX", "fr", undefined, null, 1]) {
+      expect(isLocale(value)).toBe(false)
+    }
+  })
+
+  it("resolves valid locale cookie values and falls back to the configured default for invalid values", () => {
+    expect(resolveLocale("es", "en")).toBe("es")
+    expect(resolveLocale("en", "es")).toBe("en")
+
+    for (const value of ["", "ES", "es-MX", "fr", undefined, null, 1]) {
+      expect(resolveLocale(value, "es")).toBe("es")
+      expect(resolveLocale(value, "en")).toBe("en")
+    }
+  })
+
+  it("resolves the configured default locale from env-like values with a safe English fallback", () => {
+    expect(resolveDefaultLocale("es")).toBe("es")
+    expect(resolveDefaultLocale("en")).toBe("en")
+
+    for (const value of ["", "ES", "es-MX", "fr", undefined, null, 1]) {
+      expect(resolveDefaultLocale(value)).toBe("en")
+    }
+  })
+})