Fixes issue with app directory that caused problems with `i18n` was
enabled. Previously, when you accessed a URL like `/blog/first-issue`,
you would expect it to hit the app route at `/app/blog/[slug]/page.tsx`,
but instead it internally attempted to access
`/app/{defaultLocale}/blog/[slug]/page.tsx` (where `{defaultLocale}` is
set in `next.config.js` via `i18n.defaultLocale`). This is because while
the path did not assume the locale, the domain/default was enough to
suggest it, causing the mismatch.
This adds a new internal parameter for tracking this _default_
assignment so it can be handled by the matcher correctly.
Fixes#46814Fixes#46841
fix NEXT-777 ([link](https://linear.app/vercel/issue/NEXT-777))
fix NEXT-834 ([link](https://linear.app/vercel/issue/NEXT-834))
---------
Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>