{"record":{"id":"b7fae97c0b474619","repo":"vercel/next.js","slug":"specified-i18n-locales-must-be-an-array-of-locale","errorCode":null,"errorMessage":"Specified i18n.locales must be an array of locale strings e.g. [\"en-US\", \"nl-NL\"] received ${typeof i18n.locales}.\\nSee more info here: https://nextjs.org/docs/messages/invalid-i18n-config","messagePattern":"Specified i18n\\.locales must be an array of locale strings e\\.g\\. \\[\"en-US\", \"nl-NL\"\\] received (.+?)\\.\\\\nSee more info here: https://nextjs\\.org/docs/messages/invalid-i18n-config","errorType":"validation","errorClass":null,"httpStatus":null,"severity":"error","filePath":"packages/next/src/server/config.ts","lineNumber":1363,"sourceCode":"          }\n        }\n\n        return hasInvalidLocale\n      })\n\n      if (invalidDomainItems.length > 0) {\n        throw new Error(\n          `Invalid i18n.domains values:\\n${invalidDomainItems\n            .map((item: any) => JSON.stringify(item))\n            .join(\n              '\\n'\n            )}\\n\\ndomains value must follow format { domain: 'example.fr', defaultLocale: 'fr', locales: ['fr'] }.\\nSee more info here: https://nextjs.org/docs/messages/invalid-i18n-config`\n        )\n      }\n    }\n\n    if (!Array.isArray(i18n.locales)) {\n      throw new Error(\n        `Specified i18n.locales must be an array of locale strings e.g. [\"en-US\", \"nl-NL\"] received ${typeof i18n.locales}.\\nSee more info here: https://nextjs.org/docs/messages/invalid-i18n-config`\n      )\n    }\n\n    const invalidLocales = i18n.locales.filter(\n      (locale: any) => typeof locale !== 'string'\n    )\n\n    if (invalidLocales.length > 0) {\n      throw new Error(\n        `Specified i18n.locales contains invalid values (${invalidLocales\n          .map(String)\n          .join(\n            ', '\n          )}), locales must be valid locale tags provided as strings e.g. \"en-US\".\\n` +\n          `See here for list of valid language sub-tags: http://www.iana.org/assignments/language-subtag-registry/language-subtag-registry`\n      )\n    }","sourceCodeStart":1345,"sourceCodeEnd":1381,"githubUrl":"https://github.com/vercel/next.js/blob/34433fd12ee8074ea3f47af9f36255c7390d0301/packages/next/src/server/config.ts#L1345-L1381","documentation":"Error \"Specified i18n.locales must be an array of locale strings e.g. [\"en-US\", \"nl-NL\"] received ${typeof i18n.locales}.\\nSee more info here: https://nextjs.org/docs/messages/invalid-i18n-config\" thrown in vercel/next.js.","triggerScenarios":"i18n.locales is not an array of locale strings.","commonSituations":"Non-string values inside i18n.locales in next.config.","solutions":["Make every i18n.locales entry a locale string like \"en-US\"."],"exampleFix":null,"handlingStrategy":"validation","validationCode":null,"typeGuard":null,"tryCatchPattern":null,"preventionTips":[],"tags":[],"backgroundTag":null,"analyzedSha":"34433fd12ee8074ea3f47af9f36255c7390d0301","analyzedAt":"2026-08-19T02:10:13.922Z","contentChangedAt":"2026-08-19T02:10:13.922Z","schemaVersion":2},"datasetVersion":"2026-09-23T08:17:48.524Z"}