Big documentation rewrite, move docs to example site

exampleSite/content.en/docs/content/multilingual.md

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+---
+title: Multi-Language
+weight: 4
+---
+
+# Multi-Language Support
+
+Hugo Book supports Hugo's [multilingual mode](https://gohugo.io/content-management/multilingual/) with content translation by directory.
+
+## Configuration
+
+Define languages in your site config
+
+```toml {filename=hugo.toml}
+[languages]
+[languages.en]
+  label = 'English'
+  contentDir = 'content.en'
+  weight = 1
+
+[languages.zh]
+  label = 'Chinese'
+  contentDir = 'content.zh'
+  weight = 2
+
+[languages.he]
+  label = 'Hebrew'
+  contentDir = 'content.he'
+  direction = 'rtl'
+  weight = 3
+```
+
+A language selector dropdown appears automatically when multiple languages are configured.
+
+## RTL Support
+
+Set `direction = 'rtl'` on a language to enable right-to-left layout. The entire page layout, including the sidebar menu, mirrors automatically.
+
+## Translation Dropdown
+
+By default, all configured languages appear in the selector. To only show languages that have a translation for the current page
+
+```toml {filename=hugo.toml}
+[params]
+  BookTranslatedOnly = true
+```