🌐 [i18n-KO] Display English version of untranslated pages as a default option for improved UX 
Part of https://github.com/huggingface/transformers/issues/20179
### Summary

We've been collecting feedback from our users, and a common theme we've identified is concerning the user experience when encountering untranslated pages. Users have expressed a preference to see the English version of a page directly if the localized translation is not yet available. This allows them to utilize tools like Google Chrome's translation feature to understand the content. 

### Detail

#### Current Behavior:

Presently, when a user navigates to a page that hasn't been translated into their selected language, they're presented with a placeholder message indicating that the page is unavailable in their language. This leaves them without immediate access to the content they were seeking.

#### Desired Behavior:

Instead of showing a placeholder message for untranslated pages, users prefer to be automatically shown the English version of the page. This way, they can use automated translation tools if necessary. In addition, users can also choose to read the page in English if they're comfortable doing so.

### Additional Benefits

This approach provides several additional benefits:

- **Conflict mitigation:** This will likely reduce the number of merge conflicts that can occur due to manual reference edits in multiple language versions.
- **Easier Table of Contents (TOC) control:** By defaulting to English versions, we ensure that the TOC structure remains consistent across the site, providing a more predictable and streamlined user experience.

### Next Steps

We suggest implementing this feature to enhance the user experience and streamline the site's operations. This would involve modifying the behavior of the site when a page is unavailable in the selected language. We look forward to feedback and any additional perspectives on this proposed enhancement.

cc: [HF] @sgugger @ArthurZucker [PseudoLab] @0525hhgus @gabrielwithappy @sim-so @HanNayeoniee @jungnerd @KIHOON71

This should already be the case without having to do anything special. cc @mishig25 