Rewrites with i18n causes TypeError: Expected "nextInternalLocale" to be a string

Bug report

Describe the bug

Using rewrites in next.config.js together with following i18n settings:

i18n: {
  locales: ['en', 'de'],
  defaultLocale: 'de',
  localeDetection: false,
}

Rewrite example:

async rewrites() {
    const rewrites = [
      {
        source: '/gssp-alternative',
        destination: '/gssp',
      },
    ];

    return rewrites;
  },

Navigating in browser from / to /gssp-alternative causes a client-side runtime error.

To Reproduce

https://repl.it/@berndartmueller/nextjs1003-nextInternalLocale-bug

1. Click on “CLICK HERE TO SEE ERROR” link
2. Error popup is shown with error TypeError: Expected "nextInternalLocale" to be a string

Expected behavior

No error.

System information

• OS: macOS
• Browser: does not matter
• Version of Next.js: 10.0.3
• Version of Node.js: Don’t know, it’s repl.it 😄
• Deployment: next dev

Thanks a lot!

[muserref-sefer]

Please add locale: false

https://nextjs.org/docs/api-reference/next.config.js/rewrites#rewrites-with-i18n-support

[kivohin]

I encounter the exact same error when using i18n Routing + Rewrites.

I already created a bug report (#19227) for another issue when I am using i18n Routing + Rewrites + Vercel Now.

But the attached demo repository (https://github.com/kivohin/i18n-routing-rewrites-vercel-now) in that bug report can be used to reproduce the mentioned error (TypeError: Expected "nextInternalLocale" to be a string).

I still get it even when using the suggested locale: false option on Next.js v10.0.3.

@berndartmueller, @MSefer