feat: add fallback default language support

Author: sy-records

docs/configuration.md

@@ -240,6 +240,22 @@ window.$docsify = {
 };
 ```
 
+## fallbackDefaultLanguage
+
+- Type: `String`
+- Default: `''`
+
+When a page is requested and it doesn't exist for the given locale, Docsify will fallback to the language specified by this option.
+
+For example, in the scenario described above, if `/de/overview` does not exist and `fallbackDefaultLanguage` is configured as `zh-cn`, Docsify will fetch `/zh-cn/overview` instead of `/overview`.
+
+```js
+window.$docsify = {
+  fallbackLanguages: ['fr', 'de'],
+  fallbackDefaultLanguage: 'zh-cn', // default: ''
+};
+```
+
 ## formatUpdated
 
 - Type: `String|Function`
@@ -262,7 +278,7 @@ window.$docsify = {
 ## hideSidebar
 
 - Type : `Boolean`
-- Default: `true`
+- Default: `false`
 
 This option will completely hide your sidebar and won't render any content on the side.
 

src/core/config.js

@@ -7,6 +7,7 @@ const currentScript = document.currentScript;
 export default function (vm) {
   const config = Object.assign(
     {
+      alias: {},
       auto2top: false,
       autoHeader: false,
       basePath: '',
@@ -18,11 +19,16 @@ export default function (vm) {
       ext: '.md',
       externalLinkRel: 'noopener',
       externalLinkTarget: '_blank',
+      fallbackLanguages: null,
+      fallbackDefaultLanguage: '',
       formatUpdated: '',
-      ga: '',
+      hideSidebar: false,
       homepage: 'README.md',
+      keyBindings: {},
       loadNavbar: null,
       loadSidebar: null,
+      logo: false,
+      markdown: null,
       maxLevel: 6,
       mergeNavbar: false,
       name: '',
@@ -31,11 +37,14 @@ export default function (vm) {
       noCompileLinks: [],
       noEmoji: false,
       notFoundPage: false,
+      onlyCover: false,
       plugins: [],
       relativePath: false,
       repo: '',
-      routes: {},
+      requestHeaders: {},
       routerMode: 'hash',
+      routes: {},
+      skipLink: 'Skip to main content',
       subMaxLevel: 0,
       // themeColor: '',
       topMargin: 0,

src/core/fetch/index.js

@@ -204,7 +204,12 @@ export function Fetch(Base) {
     }
 
     _fetchFallbackPage(path, qs, cb = noop) {
-      const { requestHeaders, fallbackLanguages, loadSidebar } = this.config;
+      const {
+        requestHeaders,
+        fallbackLanguages,
+        fallbackDefaultLanguage,
+        loadSidebar,
+      } = this.config;
 
       if (!fallbackLanguages) {
         return false;
@@ -217,7 +222,7 @@ export function Fetch(Base) {
       }
 
       const newPath = this.router.getFile(
-        path.replace(new RegExp(`^/${local}`), ''),
+        path.replace(new RegExp(`^/${local}`), fallbackDefaultLanguage),
       );
       const req = this.#request(newPath + qs, requestHeaders);