I have a case where I need some subroutes (within the same layout tree) to support more locales than the rest of the app. So there is for example /forms directory which needs to have ['en', 'es', 'de', ...] and rest of the app requires only ['en', 'es']. The next-intl examples have mixed routing here: https://next-intl.dev/examples#app-router-mixed-routing). But that example is for “no-locale + locale” routes — not “subset vs superset” locale groups.

├─ [locale]/        
│  ├─ layout.tsx           
│  ├─ page.tsx        # (more pages like this with only en/es) 
│  └─ forms/          # (en,es,de, ...)
│     ├─ layout.tsx          
│     ├─ page.tsx
│     └─ [slug]/page.tsx

Questions:

Is there a built-in or recommended approach within next-intl for handling this “partial locale” setup?

Or should I write a custom middleware.ts that adjusts routing and detection so links work correctly when navigating between pages that have different locale availability?

Any patterns to help guide me would be helpful!