Middleware size is affected by messages in Next.js 15

[polly3d]

Description

I got an error when I deploy to Vercel. The error is: The Edge Function "src/middleware" size is 1.65 MB and your plan size limit is 1 MB. All translations are packaged into a middleware file.

I know, my translation file was big. Is there any solution for this?

Here's the screenshot of the translation files:

Here's the configuration in i18n folder:

// request.ts
import { getRequestConfig } from "next-intl/server";
import { routing } from "./routing";

export default getRequestConfig(async ({ requestLocale }) => {
  // This typically corresponds to the `[locale]` segment
  let locale = await requestLocale;

  // Ensure that a valid locale is used
  if (!locale || !routing.locales.includes(locale as any)) {
    locale = routing.defaultLocale;
  }

  return {
    locale,
    messages: (await import(`../locales/${locale}.json`)).default,
  };
});

// routing.ts
import { defineRouting } from "next-intl/routing";
import { createNavigation } from "next-intl/navigation";

export const routing = defineRouting({
  // A list of all locales that are supported
  locales: ["en", "es"],
  localePrefix: "as-needed",
  // Used when no locale matches
  defaultLocale: "en",
});

// Lightweight wrappers around Next.js' navigation APIs
// that will consider the routing configuration
export const { Link, redirect, usePathname, useRouter, getPathname } =
  createNavigation(routing);

The middleware:

import createMiddleware from "next-intl/middleware";
import { routing } from "./i18n/routing";

export default createMiddleware(routing);

export const config = {
  matcher: [
    // Skip Next.js internals and all static files, unless found in search params
    "/((?!_next|monitoring|[^?]*\\.(?:html?|css|js(?!on)|jpe?g|webp|png|gif|svg|ttf|woff2?|ico|csv|docx?|xlsx?|zip|webmanifest|xml|txt)).*)",
    // Always run for API routes
    "/(api|trpc)(.*)",
  ],
};

Verifications

• I've verified that the problem I'm experiencing isn't covered in the docs.
• I've searched for similar, existing issues on GitHub and Stack Overflow.
• I've compared my app to a working example to look for differences.

Mandatory reproduction URL

None

Reproduction description

None

Expected behaviour

Reduce middleware file size

[github-actions]

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[polly3d]

I'm sorry.

Here's the reproduction link:

https://github.com/polly3d/next-intl-json

Hope it's helpful. And let me know if anything else you need.

[amannn]

Thanks for the reproduction!

It seems like Next.js 15 has changed something with the bundling behavior, I need to dig a bit deeper and potentially create a bug report upstream. I've confirmed that with Next.js 14 this is not the case.

As a quick fix, you can split this out from your routing.ts:

// i18n/navigation.ts

import {createNavigation} from 'next-intl/navigation';
import {routing} from './routing';

export const {Link, redirect, usePathname, useRouter, getPathname} =
  createNavigation(routing);

With this, your middleware size will not be affected anymore.

[amannn]

I've talked to the Next.js team via DM and they confirmed suspicious behavior in Next.js here. I've added an upstream report here: vercel/next.js#75180.

As a workaround for the time being, please consider #1669 (comment).

[polly3d]

Thank you so much for your quick help!

It's fixed.

[amannn]

Sure, you're welcome! I'll leave the issue open as I'm currently waiting for the Next.js team to hopefully address this upstream.