{"record":{"id":"032b3a3d4c21beea","repo":"vercel/next.js","slug":"specified-i18n-localedetection-should-be-undefined","errorCode":null,"errorMessage":"Specified i18n.localeDetection should be undefined or a boolean received ${localeDetectionType}.\\nSee more info here: https://nextjs.org/docs/messages/invalid-i18n-config","messagePattern":"Specified i18n\\.localeDetection should be undefined or a boolean received (.+?)\\.\\\\nSee more info here: https://nextjs\\.org/docs/messages/invalid-i18n-config","errorType":"validation","errorClass":null,"httpStatus":null,"severity":"error","filePath":"packages/next/src/server/config.ts","lineNumber":1421,"sourceCode":"          `${[...duplicateLocales].join(', ')}\\n` +\n          `Each locale should be listed only once.\\n` +\n          `See more info here: https://nextjs.org/docs/messages/invalid-i18n-config`\n      )\n    }\n\n    // make sure default Locale is at the front\n    i18n.locales = [\n      i18n.defaultLocale,\n      ...i18n.locales.filter((locale) => locale !== i18n.defaultLocale),\n    ]\n\n    const localeDetectionType = typeof i18n.localeDetection\n\n    if (\n      localeDetectionType !== 'boolean' &&\n      localeDetectionType !== 'undefined'\n    ) {\n      throw new Error(\n        `Specified i18n.localeDetection should be undefined or a boolean received ${localeDetectionType}.\\nSee more info here: https://nextjs.org/docs/messages/invalid-i18n-config`\n      )\n    }\n  }\n\n  if (result.devIndicators !== false && result.devIndicators?.position) {\n    const { position } = result.devIndicators\n    const allowedValues = [\n      'top-left',\n      'top-right',\n      'bottom-left',\n      'bottom-right',\n    ]\n\n    if (!allowedValues.includes(position)) {\n      throw new Error(\n        `Invalid \"devIndicator.position\" provided, expected one of ${allowedValues.join(\n          ', '","sourceCodeStart":1403,"sourceCodeEnd":1439,"githubUrl":"https://github.com/vercel/next.js/blob/34433fd12ee8074ea3f47af9f36255c7390d0301/packages/next/src/server/config.ts#L1403-L1439","documentation":"Error \"Specified i18n.localeDetection should be undefined or a boolean received ${localeDetectionType}.\\nSee more info here: https://nextjs.org/docs/messages/invalid-i18n-config\" thrown in vercel/next.js.","triggerScenarios":"i18n.localeDetection is neither undefined nor a boolean.","commonSituations":"A string or number assigned to i18n.localeDetection in next.config.","solutions":["Set i18n.localeDetection to a boolean or remove it."],"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"}