fix architecture and write new tests

apps/marketplace/src/lib/i18n.server.test.ts

@@ -0,0 +1,41 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+const cookieValues = vi.hoisted(() => new Map<string, string>())
+
+vi.mock('next/headers', () => ({
+  cookies: async () => ({
+    get: (name: string) => {
+      const value = cookieValues.get(name)
+      return value === undefined ? undefined : { value }
+    },
+  }),
+}))
+
+import { getMarketplaceLanguage } from './i18n.server'
+import { MARKETPLACE_LANGUAGE_COOKIE, SHARED_LANGUAGE_COOKIE } from './i18n'
+
+describe('getMarketplaceLanguage', () => {
+  beforeEach(() => {
+    cookieValues.clear()
+  })
+
+  it('prefers the shared language cookie over the legacy marketplace cookie', async () => {
+    cookieValues.set(SHARED_LANGUAGE_COOKIE, 'ar')
+    cookieValues.set(MARKETPLACE_LANGUAGE_COOKIE, 'fr')
+
+    await expect(getMarketplaceLanguage()).resolves.toBe('ar')
+  })
+
+  it('falls back to the legacy marketplace cookie during migration', async () => {
+    cookieValues.set(MARKETPLACE_LANGUAGE_COOKIE, 'fr')
+
+    await expect(getMarketplaceLanguage()).resolves.toBe('fr')
+  })
+
+  it('defaults to English when cookies are absent or invalid', async () => {
+    await expect(getMarketplaceLanguage()).resolves.toBe('en')
+    cookieValues.set(SHARED_LANGUAGE_COOKIE, 'es')
+
+    await expect(getMarketplaceLanguage()).resolves.toBe('en')
+  })
+})