add handling to resolveRoutes instead

Author: ztanner

packages/next/src/server/lib/router-utils/resolve-routes.ts

@@ -395,6 +395,17 @@ export function getResolveRoutes(
               normalized = normalizers.postponed.normalize(normalized, true)
             }
 
+            if (config.i18n) {
+              const curLocaleResult = normalizeLocalePath(
+                normalized,
+                config.i18n.locales
+              )
+
+              if (curLocaleResult.detectedLocale) {
+                parsedUrl.query.__nextLocale = curLocaleResult.detectedLocale
+              }
+            }
+
             // If we updated the pathname, and it had a base path, re-add the
             // base path.
             if (updated) {

packages/next/src/shared/lib/i18n/normalize-locale-path.ts

@@ -17,17 +17,8 @@ export function normalizeLocalePath(
   locales?: string[]
 ): PathLocale {
   let detectedLocale: string | undefined
-  const isDataRoute = pathname.startsWith('/_next/data')
-
-  // Create a pathname for locale detection, removing /_next/data/[buildId] if present
-  // This is because locale detection relies on path splitting and so the first part
-  // should be the locale.
-  const pathNameNoDataPrefix = isDataRoute
-    ? pathname.replace(/^\/_next\/data\/[^/]+/, '')
-    : pathname
-
-  // Split the path for locale detection
-  const pathnameParts = pathNameNoDataPrefix.split('/')
+  // first item will be empty string from splitting at first char
+  const pathnameParts = pathname.split('/')
 
   ;(locales || []).some((locale) => {
     if (
@@ -36,17 +27,12 @@ export function normalizeLocalePath(
     ) {
       detectedLocale = locale
       pathnameParts.splice(1, 1)
+      pathname = pathnameParts.join('/') || '/'
       return true
     }
     return false
   })
 
-  // For non-data routes, we return the path with the locale stripped out.
-  // For data routes, we keep the path as is, since we only want to extract the locale.
-  if (detectedLocale && !isDataRoute) {
-    pathname = pathnameParts.join('/') || '/'
-  }
-
   return {
     pathname,
     detectedLocale,