fix(translation): prevent duplicate locale error on server restart (medusajs#14345)

The translation module's defaults loader throws a warning on every server
restart after the first run because the upsert method uses `id` as the
unique key, but defaultLocales only contains `code` and `name`.

This causes the upsert to always attempt creation, which fails on the
unique `code` constraint with: "Locale with code: en-US, already exists."

Fix: Fetch existing locales first and map their IDs into defaultLocales
so upsert can properly identify existing records and update them.

Author: 0xFl4g

.changeset/frank-days-start.md

@@ -0,0 +1,5 @@
+---
+"@medusajs/translation": patch
+---
+
+fix(translation): prevent duplicate locale error on server restart

packages/modules/translation/src/loaders/defaults.ts

@@ -3,7 +3,10 @@ import {
   Logger,
   ModulesSdkTypes,
 } from "@medusajs/framework/types"
-import { ContainerRegistrationKeys } from "@medusajs/framework/utils"
+import {
+  ContainerRegistrationKeys,
+  normalizeLocale,
+} from "@medusajs/framework/utils"
 import Locale from "@models/locale"
 
 /**
@@ -70,7 +73,24 @@ export default async ({ container }: LoaderOptions): Promise<void> => {
     container.resolve("localeService")
 
   try {
-    const resp = await localeService_.upsert(defaultLocales)
+    // Fetch existing locales to map their IDs for upsert
+    // The upsert method uses `id` as the key, so we need to include IDs for existing locales
+    const existingLocales = await localeService_.list(
+      {},
+      { select: ["id", "code"] }
+    )
+    const existingByCode = new Map(
+      existingLocales.map((l) => [l.code, l.id])
+    )
+
+    // Map default locales to include IDs for existing ones
+    const localesToUpsert = defaultLocales.map((locale) => {
+      const normalizedCode = normalizeLocale(locale.code)
+      const existingId = existingByCode.get(normalizedCode)
+      return existingId ? { ...locale, id: existingId } : locale
+    })
+
+    const resp = await localeService_.upsert(localesToUpsert)
     logger.debug(`Loaded ${resp.length} locales`)
   } catch (error) {
     logger.warn(