Azure B2C TrustFrameworkLocalization.xml extract into different files

I have TrustFrameworkLocalization.xml file, that has for now 2 languages en and de. Something like this:

<LocalizedResources Id="api.localaccountsignup.en">
    <LocalizedStrings>
        <LocalizedString ElementType="ClaimType" ElementId="email" StringId="DisplayName">Email Address</LocalizedString>
        <!-- many others -->
    </LocalizedStrings>
</LocalizedResources>

<LocalizedResources Id="api.localaccountsignup.de">
    <LocalizedStrings>
        <LocalizedString ElementType="ClaimType" ElementId="email" StringId="DisplayName">E-Mail Adresse</LocalizedString>
        <!-- many others -->
    </LocalizedStrings>
</LocalizedResources>

It works all file! So far file contains 167 rows, which is maintainable. But my client wants to extent language support and add 12 more languages. Which will make file huge and probably not easily maintainable. Is there any way to split it into different files?

Policy Hierarchy

Yes, you can set up custom policies so they inherit from another custom policy, creating a chain or hierarchy.

Say you have a custom policy B2C_1A_Base with all your technical profiles and user journeys in, and a custom policy B2C_1A_SignUpSignIn with your relying party definition that executes a sign-up/sign-in journey. You can insert policies between them and you could, for example, have one policy per language, e.g.:

B2C_1A_Base - defines everything used across all child policies.

<TrustFrameworkPolicy
   xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
   xmlns:xsd="https://www.w3.org/2001/XMLSchema"
   xmlns="http://schemas.microsoft.com/online/cpim/schemas/2013/06"
   PolicySchemaVersion="0.3.0.0"
   TenantId="yourtenant.onmicrosoft.com"
   PolicyId="B2C_1A_Base"
   PublicPolicyUri="http://yourtenant.onmicrosoft.com/B2C_1A_Base">

  <!-- Technical profiles, etc -->

</TrustFrameworkPolicy>

B2C_1A_Translations_En - inherits everything from B2C_1A_Base, overriding localisation of api.localaccountsignup.en.

<TrustFrameworkPolicy
   xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
   xmlns:xsd="https://www.w3.org/2001/XMLSchema"
   xmlns="http://schemas.microsoft.com/online/cpim/schemas/2013/06"
   PolicySchemaVersion="0.3.0.0"
   TenantId="yourtenant.onmicrosoft.com"
   PolicyId="B2C_1A_Translations_En"
   PublicPolicyUri="http://yourtenant.onmicrosoft.com/B2C_1A_Translations_En">

  <BasePolicy>
    <TenantId>yourtenant.onmicrosoft.com</TenantId>
    <PolicyId>B2C_1A_Base</PolicyId>
  </BasePolicy>

  <LocalizedResources Id="api.localaccountsignup.en">
    <LocalizedStrings>
      <LocalizedString ElementType="ClaimType" ElementId="email" StringId="DisplayName">Email Address</LocalizedString>
      <!-- many others -->
    </LocalizedStrings>
  </LocalizedResources>

</TrustFrameworkPolicy>

B2C_1A_Translations_De - inherits everything from B2C_1A_Translations_En, overriding localisation of api.localaccountsignup.de.

<TrustFrameworkPolicy
   xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
   xmlns:xsd="https://www.w3.org/2001/XMLSchema"
   xmlns="http://schemas.microsoft.com/online/cpim/schemas/2013/06"
   PolicySchemaVersion="0.3.0.0"
   TenantId="yourtenant.onmicrosoft.com"
   PolicyId="B2C_1A_Translations_De"
   PublicPolicyUri="http://yourtenant.onmicrosoft.com/B2C_1A_Translations_De">

  <BasePolicy>
    <TenantId>yourtenant.onmicrosoft.com</TenantId>
    <PolicyId>B2C_1A_Translations_En</PolicyId>
  </BasePolicy>

  <LocalizedResources Id="api.localaccountsignup.de">
    <LocalizedStrings>
      <LocalizedString ElementType="ClaimType" ElementId="email" StringId="DisplayName">E-Mail Adresse</LocalizedString>
      <!-- many others -->
    </LocalizedStrings>
  </LocalizedResources>

</TrustFrameworkPolicy>

B2C_1A_SignUpSignIn - inherits everything from B2C_1A_Translations_De, providing an entry point for relying parties with all translations available.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<TrustFrameworkPolicy
  xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
  xmlns:xsd="https://www.w3.org/2001/XMLSchema"
  xmlns="http://schemas.microsoft.com/online/cpim/schemas/2013/06"
  PolicySchemaVersion="0.3.0.0"
  TenantId="your-tenant.onmicrosoft.com"
  PolicyId="B2C_1A_SignUpSignIn"
  PublicPolicyUri="http://your-tenant.onmicrosoft.com/B2C_1A_SignUpSignIn">

  <BasePolicy>
    <TenantId>your-tenant.onmicrosoft.com</TenantId>
    <PolicyId>B2C_1A_Translations_De</PolicyId>
  </BasePolicy>

  <RelyingParty>
    <DefaultUserJourney ReferenceId="SignUpOrSignIn" />
    <TechnicalProfile Id="PolicyProfile">
      <DisplayName>PolicyProfile</DisplayName>
      <Description>The policy profile</Description>
      <Protocol Name="OpenIdConnect" />
      <OutputClaims>
        <OutputClaim ClaimTypeReferenceId="objectId" PartnerClaimType="sub"/>
        <!-- claims -->
      </OutputClaims>
      <SubjectNamingInfo ClaimType="sub" />
    </TechnicalProfile>
  </RelyingParty>
</TrustFrameworkPolicy

Note each custom policy can only have one parent and you're limited to 10 levels of inheritance, so you'll probably need to have multiple languages per file.

Deploy-time modification

Alternatively, if you're using build pipelines and Graph API to deploy the custom policies to your B2C tenant you could have the translations stored externally (e.g. in JSON files) and have a build task that reads those files, converts the appropriate content to custom policy XML and inserts them into a policy file before deploying it to B2C.