fix(i18n): revert strict structure, implement dynamic index, and duplicate ID meta

pages/index.en.mdx

@@ -1,3 +0,0 @@
-import { LandingPage } from '../components/LandingPage'
-
-<LandingPage />

pages/index.id.mdx

@@ -1,5 +1,11 @@
+import { useRouter } from 'next/router'
 import { LandingPage } from '../components/LandingPage'
 
-<LandingPage locale="id" />
+export const Index = () => {
+  const { locale } = useRouter()
+  return <LandingPage locale={locale} />
+}
+
+<Index />
 
 # DEBUG_ID_FILE_RENDERED

pages/index.mdx

@@ -0,0 +1,9 @@
+import { useRouter } from 'next/router'
+import { LandingPage } from '../components/LandingPage'
+
+export const Index = () => {
+  const { locale } = useRouter()
+  return <LandingPage locale={locale} />
+}
+
+<Index />