Since External Guidance functionality is exposed on external tools, we want to evaluate how those work on a realistic environment early. For that purpose, it may be useful to deploy the initial versions of the extension to support a language pair that (a) is exposed to a reduced number of users, and (b) is useful to prepare the next deployments.
Supporting translations from "Simple English" to "Indonesian" seem a good candidate for this deployment. Simple English results make it easy to visualize how English translations will work in the future,while being less visible in search engines.