I believe that the reason Shopify deletes your file and hides the dropdown is that Contextual Overrides (Market-specific layouts) are restricted to the “Advanced” and “Shopify Plus” plans.
If the store with the missing option is on the Basic or Standard plan, Shopify actively blocks this feature.
Your store does not have the feature that lets you create theme files for each market.
When this feature is missing, Shopify automatically deletes any market-specific file you try to add.
Why some stores have the option and others don’t
Because Theme Customizations by Market is not enabled for all stores.
It depends on:
The store’s Shopify plan
Whether Markets Pro is enabled
Shopify’s gradual rollout of the feature
How to fix it
Contact Shopify Support and ask them:
“Please enable Theme Customizations by Market for my store.”
Once they enable it, you’ll be able to create files like: index.context.belgique.json
The reason Shopify keeps deleting your file is because theme customization per market is only available on Advanced or Plus plans. That’s why you’re seeing some stores have this option and others don’t - it comes down to which plan they’re on.
If you’re on Basic or Grow, the context files for specific markets won’t work. Shopify just removes them because the feature isn’t enabled for your store.
You’d need to upgrade to at least Advanced (€289/month) to be able to create market-specific theme customizations like index.context.belgique.json.
If upgrading isn’t an option right now, one workaround is to use Shopify’s built-in localization features or conditional logic in your theme code to show different content based on the customer’s location, but it’s more manual and limited compared to the proper market contextualization.