Update Japanese translation (#508)

I'm not familiar with vitepress, so there may be some mistakes in the
settings.

website/docs/.vitepress/locales/index.ts

@@ -4,6 +4,7 @@ import zh_CN from './zh_CN'
 import zh_TW from './zh_TW'
 import vi_VN from './vi_VN'
 import id_ID from './id_ID'
+import ja_JP from './ja_JP'
 
 export default defineConfig({
   locales: {
@@ -25,6 +26,12 @@ export default defineConfig({
       themeConfig: zh_TW.themeConfig,
       description: zh_TW.description
     },
+    ja_JP: {
+      label: '日本語',
+      lang: ja_JP.lang,
+      themeConfig: ja_JP.themeConfig,
+      description: ja_JP.description
+    },
     vi_VN: {
       label: 'Tiếng Việt',
       lang: vi_VN.lang,

website/docs/.vitepress/locales/ja_JP.ts

@@ -0,0 +1,60 @@
+import { createRequire } from 'module'
+import { defineConfig } from 'vitepress'
+
+const require = createRequire(import.meta.url)
+const pkg = require('vitepress/package.json')
+
+export default defineConfig({
+  lang: 'ja-JP',
+  description: 'Android GKI デバイス向けのカーネルベースの root ソリューション',
+
+  themeConfig: {
+    nav: nav(),
+
+    lastUpdatedText: '最終更新',
+
+    sidebar: {
+      '/ja_JP/guide/': sidebarGuide()
+    },
+
+    socialLinks: [
+      { icon: 'github', link: 'https://github.com/tiann/KernelSU' }
+    ],
+
+    footer: {
+      message: 'GPL3 ライセンスでリリースされています。',
+      copyright: 'Copyright © 2022-present KernelSU Developers'
+    },
+
+    editLink: {
+      pattern: 'https://github.com/tiann/KernelSU/edit/main/website/docs/:path',
+      text: 'GitHub でこのページを編集'
+    }
+  }
+})
+
+function nav() {
+  return [
+    { text: 'ガイド', link: '/ja_JP/guide/what-is-kernelsu' },
+    { text: 'Github', link: 'https://github.com/tiann/KernelSU' }
+  ]
+}
+
+function sidebarGuide() {
+  return [
+    {
+      text: 'ガイド',
+      items: [
+        { text: 'KernelSU とは?', link: '/ja_JP/guide/what-is-kernelsu' },
+        { text: 'インストール', link: '/ja_JP/guide/installation' },
+        { text: 'ビルドするには?', link: '/guide/how-to-build' },
+        { text: '非 GKI デバイスでの実装', link: '/guide/how-to-integrate-for-non-gki' },
+        { text: '非公式の対応デバイス', link: '/ja_JP/guide/unofficially-support-devices.md' },
+        { text: 'モジュールのガイド', link: '/ja_JP/guide/module.md' },
+        { text: 'ブートループからの復旧', link: '/ja_JP/guide/rescue-from-bootloop.md' },
+        { text: 'よくある質問', link: '/ja_JP/guide/faq' },
+        { text: '隠し機能', link: '/ja_JP/guide/hidden-features' },
+      ]
+    }
+  ]
+}