Sanity Desk - How to Change the Localization Version of the Document?

I can see the issue you're facing! When using the @sanity/document-internationalization plugin (or similar i18n plugins), translated documents get their own _id with a language suffix (like frontpage__i18n_en, frontpage__i18n_no, etc.), but your desk structure is hardcoded to look for documentId("frontpage"). When you switch languages, the URL changes to the translated document's ID, resulting in a blank page because your structure doesn't account for these ID variations.

Here are a few solutions:

Solution 1: Use a filter instead of hardcoded documentId

Instead of specifying a fixed documentId, use a filter to match the base document and its translations:

S.listItem()
  .title("Home Page")
  .icon(GoHome)
  .child(
    S.documentList()
      .title("Home Page")
      .filter('_id in ["frontpage", "frontpage__i18n_*"] && _type == "page"')
      .child(documentId =>
        S.document()
          .documentId(documentId)
          .schemaType("page")
          .views([
            S.view.form(),
            S.view
              .component(Iframe)
              .options({ url: (doc) => resolveProductionUrl(doc) })
              .title("Preview"),
          ])
      )
  )

Solution 2: Extract the base ID in your preview function

If you want to keep the singleton structure, modify your resolveProductionUrl function to handle the i18n suffix. Most i18n plugins follow a pattern where the base ID is before the __i18n suffix:

function resolveProductionUrl(doc) {
  // Extract base ID by removing __i18n suffix
  const baseId = doc._id.split('__i18n')[0];
  
  // Use baseId or doc._id depending on your preview needs
  // and extract language from doc.__i18n_lang or similar field
  const language = doc.__i18n?.lang || 'en';
  
  return `https://yoursite.com/${language}/${baseId}`;
}

Solution 3: Use the plugin's helper functions

The @sanity/document-internationalization plugin typically provides helper functions like getBaseIdFromId(). Check your plugin's documentation for these utilities:

import { getBaseIdFromId } from '@sanity/document-internationalization'

S.view
  .component(Iframe)
  .options({ 
    url: (doc) => {
      const baseId = getBaseIdFromId(doc._id);
      return resolveProductionUrl({ ...doc, _id: baseId });
    }
  })
  .title("Preview")

The root cause is that your structure needs to be aware that "frontpage" isn't just one document anymore—it's a family of documents with language variations. The first solution (using a filter) is generally the most robust as it lets Sanity's desk handle the document switching naturally.

For more context on localization patterns in Sanity, check out the localization documentation which covers both document-level and field-level approaches.