See Fallback Languages in Optimizely Graph | Optimizely Developer Com

Fallback language isn't supported in Graph at the moment

Hi Kevin,

As Eric mentioned Optimizely Graph does not currently support CMS-style fallback languages automatically (like CMS 12 fallback / language branching). This is expected behavior and often causes confusion.

How language fallback works (and doesn’t work) in Optimizely Graph

In CMS:

• Language fallback is handled by the CMS runtime.

• If content doesn’t exist in the requested language, CMS transparently falls back to the configured fallback language.

In Optimizely Graph:

• Graph is language-explicit.

• If you query for sv and the content doesn’t exist in sv, Graph will simply return null.

• There is no built-in concept of “try fallback language automatically.”

So Graph will never implicitly fall back to another language for you.

If you are using PaaS CMS then this is a solvable problem using the IContentApiModelProperty interface.  Implementing this interface allows you to index custom properties within Graph and I do have PaaS clients where we do this for several fields to make querying a lot easier and to solve a very similar issue.  Lets start by looking at this interface:

public interface IContentApiModelProperty
{
    string Name { get; }

    object GetValue(ContentApiModel contentApiModel);
}

The name propety is the name of the field you want to index, this should be a unique field name to avoid confusion down the line.  The Get method is how you retrieve the value to index and is called automatically during the indexing event.

[ServiceConfiguration(typeof(IContentApiModelProperty), Lifecycle = ServiceInstanceScope.Singleton)]
public sealed class AvailableLanguagesProperty(
    IContentLoader contentLoader,
    IContentLanguageSettingsHandler contentLanguageSettingsHandler) : IContentApiModelProperty
{
    public string Name => "AvailableLanguages";

    public object GetValue(ContentApiModel contentApiModel)
    {
        return this.GetTypedValue(contentApiModel);
    }

    private IEnumerable<string> GetTypedValue(ContentApiModel contentApiModel)
    {
        if (!contentLoader.TryGet(contentApiModel.ContentLink?.ToContentReference(), out BasePageData basePageData))
        {
            return [];
        }

        var availableLanguages = new List<string>();

        // Use basePageData and IContentLanguageSettingsHandler to populate availableLanguages

        return availableLanguages..Distinct();
    }
}

This then allows us to filter our queries by our custom field for available languages, in this example we get content in en-US which is a fallback from en-GB using pure graphql, you can translate this into the library of your own chosing:

query MyQuery {
  BasePageData(where: { AvailableLanguages: { in: "en-US" } }) {
    items {
      Name
      ContentLink {
        Url
        Id
      }
      AvailableLanguages
    }
  }
}