fix: fallbackLocale not respecting default settings, locale specific fallbacks and not respecting 'none' or false (#8591)

This PR fixes and improves a few things around localisation and
fallbackLocale:
- For the REST API `fallbackLocale` and `fallback-locale` are treated
the same for consistency with the Local API
- `fallback: false` in config is now respected, by default results will
not fallback to `defaultLocale` unless this config is true, can also be
overridden by providing an explicit `fallbackLocale` in the request
- locale specific fallbacks will now take priority over `defaultLocale`
unless an explicit fallback is provided
- Fixes types on operations to allow `'none'` as a value for
fallbackLocale
- `fallback` is now true by default if unspecified

Closes https://github.com/payloadcms/payload/issues/8443

docs/configuration/localization.mdx

@@ -65,7 +65,7 @@ export default buildConfig({
       },
     ],
     defaultLocale: 'en', // required
-    fallback: true,
+    fallback: true, // defaults to true
   },
 })
 ```
@@ -81,7 +81,7 @@ The following options are available:
 | -------------- | ------------------------------------------------------------------------------------------------------------------------------ |
 | **`locales`**  | Array of all the languages that you would like to support. [More details](#locales)                                            |
 | **`defaultLocale`** | Required string that matches one of the locale codes from the array provided. By default, if no locale is specified, documents will be returned in this locale. |
-| **`fallback`** | Boolean enabling "fallback" locale functionality. If a document is requested in a locale, but a field does not have a localized value corresponding to the requested locale, then if this property is enabled, the document will automatically fall back to the fallback locale value. If this property is not enabled, the value will not be populated. |
+| **`fallback`** | Boolean enabling "fallback" locale functionality. If a document is requested in a locale, but a field does not have a localized value corresponding to the requested locale, then if this property is enabled, the document will automatically fall back to the fallback locale value. If this property is not enabled, the value will not be populated unless a fallback is explicitly provided in the request. True by default. |
 
 ### Locales
 

examples/multi-tenant/src/app/components/Login/client.page.tsx

@@ -20,7 +20,9 @@ export const Login = ({ tenantSlug }: Props) => {
 
   const handleSubmit = async (e: FormEvent) => {
     e.preventDefault()
-    if (!usernameRef?.current?.value || !passwordRef?.current?.value) {return}
+    if (!usernameRef?.current?.value || !passwordRef?.current?.value) {
+      return
+    }
     const actionRes = await fetch(
       `${process.env.NEXT_PUBLIC_SERVER_URL}/api/users/external-users/login`,
       {

examples/multi-tenant/src/collections/Pages/hooks/ensureUniqueSlug.ts

@@ -6,7 +6,9 @@ import { getTenantAccessIDs } from '../../../utilities/getTenantAccessIDs'
 
 export const ensureUniqueSlug: FieldHook = async ({ data, originalDoc, req, value }) => {
   // if value is unchanged, skip validation
-  if (originalDoc.slug === value) {return value}
+  if (originalDoc.slug === value) {
+    return value
+  }
 
   const incomingTenantID = typeof data?.tenant === 'object' ? data.tenant.id : data?.tenant
   const currentTenantID =

examples/multi-tenant/src/collections/Pages/index.ts

@@ -14,7 +14,9 @@ export const Pages: CollectionConfig = {
     read: (args) => {
       // when viewing pages inside the admin panel
       // restrict access to the ones your user has access to
-      if (isPayloadAdminPanel(args.req)) {return filterByTenantRead(args)}
+      if (isPayloadAdminPanel(args.req)) {
+        return filterByTenantRead(args)
+      }
 
       // when viewing pages from outside the admin panel
       // you should be able to see your tenants and public tenants

examples/multi-tenant/src/collections/Tenants/access/read.ts

@@ -7,7 +7,9 @@ export const tenantRead: Access = (args) => {
   const req = args.req
 
   // Super admin can read all
-  if (isSuperAdmin(args)) {return true}
+  if (isSuperAdmin(args)) {
+    return true
+  }
 
   const tenantIDs = getTenantAccessIDs(req.user)
 

examples/multi-tenant/src/collections/Users/access/create.ts

@@ -7,13 +7,19 @@ import { getTenantAdminTenantAccessIDs } from '../../../utilities/getTenantAcces
 
 export const createAccess: Access<User> = (args) => {
   const { req } = args
-  if (!req.user) {return false}
+  if (!req.user) {
+    return false
+  }
 
-  if (isSuperAdmin(args)) {return true}
+  if (isSuperAdmin(args)) {
+    return true
+  }
 
   const adminTenantAccessIDs = getTenantAdminTenantAccessIDs(req.user)
 
-  if (adminTenantAccessIDs.length > 0) {return true}
+  if (adminTenantAccessIDs.length > 0) {
+    return true
+  }
 
   return false
 }

examples/multi-tenant/src/collections/Users/access/isAccessingSelf.ts

@@ -1,6 +1,8 @@
 import type { Access } from 'payload'
 
 export const isAccessingSelf: Access = ({ id, req }) => {
-  if (!req?.user) {return false}
+  if (!req?.user) {
+    return false
+  }
   return req.user.id === id
 }

examples/multi-tenant/src/collections/Users/access/updateAndDelete.ts

@@ -5,9 +5,13 @@ import { getTenantAdminTenantAccessIDs } from '../../../utilities/getTenantAcces
 
 export const updateAndDeleteAccess: Access = (args) => {
   const { req } = args
-  if (!req.user) {return false}
+  if (!req.user) {
+    return false
+  }
 
-  if (isSuperAdmin(args)) {return true}
+  if (isSuperAdmin(args)) {
+    return true
+  }
 
   const adminTenantAccessIDs = getTenantAdminTenantAccessIDs(req.user)
 

examples/multi-tenant/src/collections/Users/hooks/ensureUniqueUsername.ts

@@ -6,7 +6,9 @@ import { getTenantAccessIDs } from '../../../utilities/getTenantAccessIDs'
 
 export const ensureUniqueUsername: FieldHook = async ({ data, originalDoc, req, value }) => {
   // if value is unchanged, skip validation
-  if (originalDoc.username === value) {return value}
+  if (originalDoc.username === value) {
+    return value
+  }
 
   const incomingTenantID = typeof data?.tenant === 'object' ? data.tenant.id : data?.tenant
   const currentTenantID =

examples/multi-tenant/src/fields/TenantField/hooks/autofillTenant.ts

@@ -8,7 +8,9 @@ export const autofillTenant: FieldHook = ({ req, value }) => {
   // return that tenant ID as the value
   if (!value) {
     const tenantIDs = getTenantAccessIDs(req.user)
-    if (tenantIDs.length === 1) {return tenantIDs[0]}
+    if (tenantIDs.length === 1) {
+      return tenantIDs[0]
+    }
   }
 
   return value

examples/multi-tenant/src/fields/TenantField/index.ts

@@ -10,7 +10,9 @@ export const tenantField: Field = {
   access: {
     read: () => true,
     update: (args) => {
-      if (isSuperAdmin(args)) {return true}
+      if (isSuperAdmin(args)) {
+        return true
+      }
       return tenantFieldUpdate(args)
     },
   },

examples/multi-tenant/src/utilities/getTenantAccessIDs.ts

@@ -1,7 +1,9 @@
 import type { User } from '../payload-types'
 
 export const getTenantAccessIDs = (user: null | User): string[] => {
-  if (!user) {return []}
+  if (!user) {
+    return []
+  }
   return (
     user?.tenants?.reduce((acc: string[], { tenant }) => {
       if (tenant) {
@@ -13,7 +15,9 @@ export const getTenantAccessIDs = (user: null | User): string[] => {
 }
 
 export const getTenantAdminTenantAccessIDs = (user: null | User): string[] => {
-  if (!user) {return []}
+  if (!user) {
+    return []
+  }
 
   return (
     user?.tenants?.reduce((acc: string[], { roles, tenant }) => {

packages/next/src/utilities/addLocalesToRequest.ts

@@ -1,5 +1,6 @@
 import type { PayloadRequest, SanitizedConfig } from 'payload'
 
+import { sanitizeFallbackLocale } from 'payload'
 /**
  * Mutates the Request to contain 'locale' and 'fallbackLocale' based on data or searchParams
  */
@@ -17,12 +18,14 @@ export function addLocalesToRequestFromData(req: PayloadRequest): void {
       localeOnReq = data.locale
     }
 
-    if (
+    if (!fallbackLocaleOnReq) {
-      !fallbackLocaleOnReq &&
+      if (data?.['fallback-locale'] && typeof data?.['fallback-locale'] === 'string') {
-      data?.['fallback-locale'] &&
+        fallbackLocaleOnReq = data['fallback-locale']
-      typeof data?.['fallback-locale'] === 'string'
+      }
-    ) {
+
-      fallbackLocaleOnReq = data['fallback-locale']
+      if (data?.['fallbackLocale'] && typeof data?.['fallbackLocale'] === 'string') {
+        fallbackLocaleOnReq = data['fallbackLocale']
+      }
     }
 
     const { fallbackLocale, locale } = sanitizeLocales({
@@ -54,15 +57,19 @@ export const sanitizeLocales = ({
   locale,
   localization,
 }: SanitizeLocalesArgs): SanitizeLocalesReturn => {
-  if (['none', 'null'].includes(fallbackLocale)) {
+  // Check if localization has fallback enabled or if a fallback locale is provided
-    fallbackLocale = 'null'
+
-  } else if (localization && !localization.localeCodes.includes(fallbackLocale)) {
+  if (localization) {
-    fallbackLocale = localization.defaultLocale
+    fallbackLocale = sanitizeFallbackLocale({
+      fallbackLocale,
+      locale,
+      localization,
+    })
   }
 
   if (locale === '*') {
     locale = 'all'
-  } else if (localization && !localization.localeCodes.includes(locale)) {
+  } else if (localization && !localization.localeCodes.includes(locale) && localization.fallback) {
     locale = localization.defaultLocale
   }
 

packages/next/src/utilities/createPayloadRequest.ts

@@ -1,7 +1,7 @@
 import type { CustomPayloadRequestProperties, PayloadRequest, SanitizedConfig } from 'payload'
 
 import { initI18n } from '@payloadcms/translations'
-import { executeAuthStrategies, getDataLoader, parseCookies } from 'payload'
+import { executeAuthStrategies, getDataLoader, parseCookies, sanitizeFallbackLocale } from 'payload'
 import * as qs from 'qs-esm'
 import { URL } from 'url'
 
@@ -26,6 +26,7 @@ export const createPayloadRequest = async ({
   const payload = await getPayloadHMR({ config: configPromise })
 
   const { config } = payload
+  const localization = config.localization
 
   const urlProperties = new URL(request.url)
   const { pathname, searchParams } = urlProperties
@@ -45,8 +46,10 @@ export const createPayloadRequest = async ({
     language,
   })
 
-  let locale
+  const fallbackFromRequest =
-  let fallbackLocale
+    searchParams.get('fallback-locale') || searchParams.get('fallbackLocale')
+  let locale = searchParams.get('locale')
+  let fallbackLocale = fallbackFromRequest
 
   const overrideHttpMethod = request.headers.get('X-HTTP-Method-Override')
   const queryToParse = overrideHttpMethod === 'GET' ? await request.text() : urlProperties.search
@@ -59,21 +62,24 @@ export const createPayloadRequest = async ({
       })
     : {}
 
-  if (config.localization) {
+  if (localization) {
-    const locales = sanitizeLocales({
+    fallbackLocale = sanitizeFallbackLocale({
-      fallbackLocale: searchParams.get('fallback-locale'),
+      fallbackLocale,
-      locale: searchParams.get('locale'),
+      locale,
-      localization: payload.config.localization,
+      localization,
     })
+
+    const locales = sanitizeLocales({
+      fallbackLocale,
+      locale,
+      localization,
+    })
+
     locale = locales.locale
-    fallbackLocale = locales.fallbackLocale
 
     // Override if query params are present, in order to respect HTTP method override
     if (query.locale) {
-      locale = query.locale
+      locale = query.locale as string
-    }
-    if (query?.['fallback-locale']) {
-      fallbackLocale = query['fallback-locale']
     }
   }
 

packages/next/src/utilities/getRequestLocales.ts

@@ -1,5 +1,7 @@
 import type { Payload } from 'payload'
 
+import { sanitizeFallbackLocale } from 'payload'
+
 type GetRequestLocalesArgs = {
   data?: Record<string, any>
   localization: Exclude<Payload['config']['localization'], false>
@@ -10,7 +12,7 @@ export function getRequestLocales({ data, localization, searchParams }: GetReque
   locale: string
 } {
   let locale = searchParams.get('locale')
-  let fallbackLocale = searchParams.get('fallback-locale')
+  let fallbackLocale = searchParams.get('fallback-locale') || searchParams.get('fallbackLocale')
 
   if (data) {
     if (data?.locale) {
@@ -19,13 +21,16 @@ export function getRequestLocales({ data, localization, searchParams }: GetReque
     if (data?.['fallback-locale']) {
       fallbackLocale = data['fallback-locale']
     }
+    if (data?.['fallbackLocale']) {
+      fallbackLocale = data['fallbackLocale']
+    }
   }
 
-  if (fallbackLocale === 'none') {
+  fallbackLocale = sanitizeFallbackLocale({
-    fallbackLocale = 'null'
+    fallbackLocale,
-  } else if (!localization.localeCodes.includes(fallbackLocale)) {
+    locale,
-    fallbackLocale = localization.defaultLocale
+    localization,
-  }
+  })
 
   if (locale === '*') {
     locale = 'all'

packages/next/src/utilities/initPage/index.ts

@@ -44,7 +44,7 @@ export const initPage = async ({
   // we get above. Clone the req? We'll look into that eventually.
   const req = await createLocalReq(
     {
-      fallbackLocale: null,
+      fallbackLocale: false,
       req: {
         headers,
         host: headers.get('host'),

packages/next/src/utilities/initReq.ts

@@ -39,7 +39,6 @@ export const initReq = cache(async function (
 
   const req = await createLocalReq(
     {
-      fallbackLocale: 'null',
       req: {
         headers,
         host: headers.get('host'),

packages/next/src/views/Document/getDocumentData.ts

@@ -26,7 +26,7 @@ export const getDocumentData = async ({
         collection: collectionSlug,
         depth: 0,
         draft: true,
-        fallbackLocale: null,
+        fallbackLocale: false,
         locale: locale?.code,
         overrideAccess: false,
         user,
@@ -38,7 +38,7 @@ export const getDocumentData = async ({
         slug: globalSlug,
         depth: 0,
         draft: true,
-        fallbackLocale: null,
+        fallbackLocale: false,
         locale: locale?.code,
         overrideAccess: false,
         user,

packages/next/src/views/Document/index.tsx

@@ -149,6 +149,7 @@ export const renderDocument = async ({
       data: doc,
       docPermissions,
       docPreferences,
+      fallbackLocale: false,
       globalSlug,
       locale: locale?.code,
       operation: (collectionSlug && id) || globalSlug ? 'update' : 'create',
@@ -278,7 +279,7 @@ export const renderDocument = async ({
       data: initialData || {},
       depth: 0,
       draft: true,
-      fallbackLocale: null,
+      fallbackLocale: false,
       locale: locale?.code,
       req,
       user,

packages/next/src/views/List/index.tsx

@@ -139,7 +139,7 @@ export const renderListView = async (
       collection: collectionSlug,
       depth: 0,
       draft: true,
-      fallbackLocale: null,
+      fallbackLocale: false,
       includeLockStatus: true,
       limit,
       locale,

packages/next/src/views/LivePreview/index.tsx

@@ -37,7 +37,7 @@ export const LivePreviewView: PayloadServerReactComponent<EditViewComponent> = a
         collection: collectionConfig.slug,
         depth: 0,
         draft: true,
-        fallbackLocale: null,
+        fallbackLocale: false,
       })
     }
 
@@ -46,7 +46,7 @@ export const LivePreviewView: PayloadServerReactComponent<EditViewComponent> = a
         slug: globalConfig.slug,
         depth: 0,
         draft: true,
-        fallbackLocale: null,
+        fallbackLocale: false,
       })
     }
   } catch (error) {

packages/payload/src/admin/forms/Form.ts

@@ -2,6 +2,7 @@ import { type SupportedLanguages } from '@payloadcms/translations'
 
 import type { DocumentPermissions } from '../../auth/types.js'
 import type { Field, Validate } from '../../fields/config/types.js'
+import type { TypedLocale } from '../../index.js'
 import type { DocumentPreferences } from '../../preferences/types.js'
 import type { PayloadRequest, Where } from '../../types/index.js'
 
@@ -62,6 +63,7 @@ export type BuildFormStateArgs = {
   data?: Data
   docPermissions: DocumentPermissions | undefined
   docPreferences: DocumentPreferences
+  fallbackLocale?: false | TypedLocale
   formState?: FormState
   id?: number | string
   /*

packages/payload/src/collections/operations/local/create.ts

@@ -28,7 +28,7 @@ export type Options<TSlug extends CollectionSlug, TSelect extends SelectType> =
   disableTransaction?: boolean
   disableVerificationEmail?: boolean
   draft?: boolean
-  fallbackLocale?: TypedLocale
+  fallbackLocale?: false | TypedLocale
   file?: File
   filePath?: string
   locale?: TypedLocale

packages/payload/src/collections/operations/local/delete.ts

@@ -22,7 +22,7 @@ export type BaseOptions<TSlug extends CollectionSlug, TSelect extends SelectType
   context?: RequestContext
   depth?: number
   disableTransaction?: boolean
-  fallbackLocale?: TypedLocale
+  fallbackLocale?: false | TypedLocale
   locale?: TypedLocale
   overrideAccess?: boolean
   overrideLock?: boolean

packages/payload/src/collections/operations/local/duplicate.ts

@@ -22,7 +22,7 @@ export type Options<TSlug extends CollectionSlug, TSelect extends SelectType> =
   depth?: number
   disableTransaction?: boolean
   draft?: boolean
-  fallbackLocale?: TypedLocale
+  fallbackLocale?: false | TypedLocale
   id: number | string
   locale?: TypedLocale
   overrideAccess?: boolean

packages/payload/src/collections/operations/local/find.ts

@@ -31,7 +31,7 @@ export type Options<TSlug extends CollectionSlug, TSelect extends SelectType> =
   depth?: number
   disableErrors?: boolean
   draft?: boolean
-  fallbackLocale?: TypedLocale
+  fallbackLocale?: false | TypedLocale
   includeLockStatus?: boolean
   joins?: JoinQuery<TSlug>
   limit?: number

packages/payload/src/collections/operations/local/findByID.ts

@@ -34,7 +34,7 @@ export type Options<
   depth?: number
   disableErrors?: TDisableErrors
   draft?: boolean
-  fallbackLocale?: TypedLocale
+  fallbackLocale?: false | TypedLocale
   id: number | string
   includeLockStatus?: boolean
   joins?: JoinQuery<TSlug>

packages/payload/src/collections/operations/local/findVersionByID.ts

@@ -16,7 +16,7 @@ export type Options<TSlug extends CollectionSlug> = {
   depth?: number
   disableErrors?: boolean
   draft?: boolean
-  fallbackLocale?: TypedLocale
+  fallbackLocale?: false | TypedLocale
   id: string
   locale?: 'all' | TypedLocale
   overrideAccess?: boolean

packages/payload/src/collections/operations/local/findVersions.ts

@@ -23,7 +23,7 @@ export type Options<TSlug extends CollectionSlug> = {
   context?: RequestContext
   depth?: number
   draft?: boolean
-  fallbackLocale?: TypedLocale
+  fallbackLocale?: false | TypedLocale
   limit?: number
   locale?: 'all' | TypedLocale
   overrideAccess?: boolean

packages/payload/src/collections/operations/local/restoreVersion.ts

@@ -14,7 +14,7 @@ export type Options<TSlug extends CollectionSlug> = {
   context?: RequestContext
   depth?: number
   draft?: boolean
-  fallbackLocale?: TypedLocale
+  fallbackLocale?: false | TypedLocale
   id: string
   locale?: TypedLocale
   overrideAccess?: boolean

packages/payload/src/collections/operations/local/update.ts

@@ -33,7 +33,7 @@ export type BaseOptions<TSlug extends CollectionSlug, TSelect extends SelectType
   depth?: number
   disableTransaction?: boolean
   draft?: boolean
-  fallbackLocale?: TypedLocale
+  fallbackLocale?: false | TypedLocale
   file?: File
   filePath?: string
   locale?: TypedLocale

packages/payload/src/config/sanitize.ts

@@ -141,6 +141,9 @@ export const sanitizeConfig = async (incomingConfig: Config): Promise<SanitizedC
         toString: () => locale.code,
       }))
     }
+
+    // Default fallback to true if not provided
+    config.localization.fallback = config.localization?.fallback ?? true
   }
 
   const i18nConfig: SanitizedConfig['i18n'] = {

packages/payload/src/config/types.ts

@@ -444,7 +444,11 @@ export type BaseLocalizationConfig = {
    * @example `"en"`
    */
   defaultLocale: string
-  /** Set to `true` to let missing values in localised fields fall back to the values in `defaultLocale` */
+  /** Set to `true` to let missing values in localised fields fall back to the values in `defaultLocale`
+   *
+   * If false, then no requests will fallback unless a fallbackLocale is specified in the request.
+   * @default true
+   */
   fallback?: boolean
 }
 

packages/payload/src/globals/operations/local/findOne.ts

@@ -16,7 +16,7 @@ export type Options<TSlug extends GlobalSlug, TSelect extends SelectType> = {
   context?: RequestContext
   depth?: number
   draft?: boolean
-  fallbackLocale?: TypedLocale
+  fallbackLocale?: false | TypedLocale
   includeLockStatus?: boolean
   locale?: 'all' | TypedLocale
   overrideAccess?: boolean

packages/payload/src/globals/operations/local/findVersionByID.ts

@@ -11,7 +11,7 @@ export type Options<TSlug extends GlobalSlug> = {
   context?: RequestContext
   depth?: number
   disableErrors?: boolean
-  fallbackLocale?: TypedLocale
+  fallbackLocale?: false | TypedLocale
   id: string
   locale?: 'all' | TypedLocale
   overrideAccess?: boolean

packages/payload/src/globals/operations/local/findVersions.ts

@@ -19,7 +19,7 @@ import { findVersionsOperation } from '../findVersions.js'
 export type Options<TSlug extends GlobalSlug> = {
   context?: RequestContext
   depth?: number
-  fallbackLocale?: TypedLocale
+  fallbackLocale?: false | TypedLocale
   limit?: number
   locale?: 'all' | TypedLocale
   overrideAccess?: boolean

packages/payload/src/globals/operations/local/restoreVersion.ts

@@ -10,7 +10,7 @@ import { restoreVersionOperation } from '../restoreVersion.js'
 export type Options<TSlug extends GlobalSlug> = {
   context?: RequestContext
   depth?: number
-  fallbackLocale?: TypedLocale
+  fallbackLocale?: false | TypedLocale
   id: string
   locale?: TypedLocale
   overrideAccess?: boolean

packages/payload/src/globals/operations/local/update.ts

@@ -19,8 +19,8 @@ export type Options<TSlug extends GlobalSlug, TSelect extends SelectType> = {
   data: DeepPartial<Omit<DataFromGlobalSlug<TSlug>, 'id'>>
   depth?: number
   draft?: boolean
-  fallbackLocale?: TypedLocale
+  fallbackLocale?: false | TypedLocale
-  locale?: TypedLocale
+  locale?: 'all' | TypedLocale
   overrideAccess?: boolean
   overrideLock?: boolean
   populate?: PopulateType

packages/payload/src/index.ts

@@ -1202,6 +1202,7 @@ export { isPlainObject } from './utilities/isPlainObject.js'
 export { isValidID } from './utilities/isValidID.js'
 export { killTransaction } from './utilities/killTransaction.js'
 export { mapAsync } from './utilities/mapAsync.js'
+export { sanitizeFallbackLocale } from './utilities/sanitizeFallbackLocale.js'
 export { traverseFields } from './utilities/traverseFields.js'
 export type { TraverseFieldsCallback } from './utilities/traverseFields.js'
 export { buildVersionCollectionFields } from './versions/buildCollectionFields.js'
@@ -1211,7 +1212,7 @@ export { deleteCollectionVersions } from './versions/deleteCollectionVersions.js
 export { enforceMaxVersions } from './versions/enforceMaxVersions.js'
 export { getLatestCollectionVersion } from './versions/getLatestCollectionVersion.js'
 export { getLatestGlobalVersion } from './versions/getLatestGlobalVersion.js'
-export { saveVersion } from './versions/saveVersion.js'
 
+export { saveVersion } from './versions/saveVersion.js'
 export type { TypeWithVersion } from './versions/types.js'
 export { deepMergeSimple } from '@payloadcms/translations/utilities'

packages/payload/src/utilities/createLocalReq.ts

@@ -1,9 +1,10 @@
 import type { User } from '../auth/types.js'
-import type { Payload, RequestContext } from '../index.js'
+import type { Payload, RequestContext, TypedLocale } from '../index.js'
 import type { PayloadRequest } from '../types/index.js'
 
 import { getDataLoader } from '../collections/dataloader.js'
 import { getLocalI18n } from '../translations/getLocalI18n.js'
+import { sanitizeFallbackLocale } from '../utilities/sanitizeFallbackLocale.js'
 
 function getRequestContext(
   req: Partial<PayloadRequest> = { context: null } as PayloadRequest,
@@ -71,7 +72,7 @@ const attachFakeURLProperties = (req: Partial<PayloadRequest>) => {
 type CreateLocalReq = (
   options: {
     context?: RequestContext
-    fallbackLocale?: string
+    fallbackLocale?: false | TypedLocale
     locale?: string
     req?: Partial<PayloadRequest>
     user?: User
@@ -83,23 +84,22 @@ export const createLocalReq: CreateLocalReq = async (
   { context, fallbackLocale, locale: localeArg, req = {} as PayloadRequest, user },
   payload,
 ) => {
-  if (payload.config?.localization) {
+  const localization = payload.config?.localization
+  if (localization) {
     const locale = localeArg === '*' ? 'all' : localeArg
-    const defaultLocale = payload.config.localization.defaultLocale
+    const defaultLocale = localization.defaultLocale
     const localeCandidate = locale || req?.locale || req?.query?.locale
 
     req.locale =
       localeCandidate && typeof localeCandidate === 'string' ? localeCandidate : defaultLocale
 
-    const fallbackLocaleFromConfig = payload.config.localization.locales.find(
+    const sanitizedFallback = sanitizeFallbackLocale({
-      ({ code }) => req.locale === code,
+      fallbackLocale,
-    )?.fallbackLocale
+      locale: req.locale,
+      localization,
+    })
 
-    if (typeof fallbackLocale !== 'undefined') {
+    req.fallbackLocale = sanitizedFallback
-      req.fallbackLocale = fallbackLocale
-    } else if (typeof req?.fallbackLocale === 'undefined') {
-      req.fallbackLocale = fallbackLocaleFromConfig || defaultLocale
-    }
   }
 
   const i18n =

packages/payload/src/utilities/sanitizeFallbackLocale.ts

@@ -0,0 +1,53 @@
+import type { SanitizedLocalizationConfig } from '../config/types.js'
+import type { TypedLocale } from '../index.js'
+
+interface Args {
+  fallbackLocale: false | TypedLocale
+  locale: string
+  localization: SanitizedLocalizationConfig
+}
+
+/**
+ * Sanitizes fallbackLocale based on a provided fallbackLocale, locale and localization config
+ *
+ * Handles the following scenarios:
+ * - determines if a fallback locale should be used
+ * - determines if a locale specific fallback should be used in place of the default locale
+ * - sets the fallbackLocale to 'null' if no fallback locale should be used
+ */
+export const sanitizeFallbackLocale = ({
+  fallbackLocale,
+  locale,
+  localization,
+}: Args): null | string => {
+  const hasFallbackLocale =
+    fallbackLocale === undefined || fallbackLocale === null
+      ? localization && localization.fallback
+      : fallbackLocale
+        ? !['false', 'none', 'null'].includes(fallbackLocale)
+        : false
+
+  if (hasFallbackLocale) {
+    if (!fallbackLocale) {
+      // Check for locale specific fallback
+      const localeSpecificFallback =
+        localization && localization?.locales?.length
+          ? localization.locales.find((localeConfig) => localeConfig.code === locale)
+              ?.fallbackLocale
+          : undefined
+
+      if (localeSpecificFallback) {
+        fallbackLocale = localeSpecificFallback
+      } else {
+        // Use defaultLocale as fallback otherwise
+        if (localization && 'fallback' in localization && localization.fallback) {
+          fallbackLocale = localization.defaultLocale
+        }
+      }
+    }
+  } else {
+    fallbackLocale = null
+  }
+
+  return fallbackLocale as null | string
+}

packages/ui/src/providers/ServerFunctions/index.tsx

@@ -84,7 +84,7 @@ export const ServerFunctionsProvider: React.FC<{
         if (!remoteSignal?.aborted) {
           const result = (await serverFunction({
             name: 'form-state',
-            args: rest,
+            args: { fallbackLocale: false, ...rest },
           })) as ReturnType<typeof buildFormStateHandler> // TODO: infer this type when `strictNullChecks` is enabled
 
           if (!remoteSignal?.aborted) {
@@ -108,7 +108,7 @@ export const ServerFunctionsProvider: React.FC<{
         if (!remoteSignal?.aborted) {
           const result = (await serverFunction({
             name: 'table-state',
-            args: rest,
+            args: { fallbackLocale: false, ...rest },
           })) as ReturnType<typeof buildTableStateHandler> // TODO: infer this type when `strictNullChecks` is enabled
 
           if (!remoteSignal?.aborted) {
@@ -132,7 +132,7 @@ export const ServerFunctionsProvider: React.FC<{
         if (!remoteSignal?.aborted) {
           const result = (await serverFunction({
             name: 'render-document',
-            args: rest,
+            args: { fallbackLocale: false, ...rest },
           })) as { docID: string; Document: React.ReactNode }
 
           if (!remoteSignal?.aborted) {