diff --git a/packages/frontend/src/config.ts b/packages/frontend/src/config.ts
index 073b21a0ae..24f60910d1 100644
--- a/packages/frontend/src/config.ts
+++ b/packages/frontend/src/config.ts
@@ -1,21 +1,22 @@
-import { miLocalStorage } from "./local-storage";
+import { miLocalStorage } from './local-storage';
 
 const address = new URL(location.href);
-const siteName = (document.querySelector('meta[property="og:site_name"]') as HTMLMetaElement)?.content;
+const siteName = document.querySelector<HTMLMetaElement>('meta[property="og:site_name"]')?.content;
 
 export const host = address.host;
 export const hostname = address.hostname;
 export const url = address.origin;
 export const apiUrl = url + '/api';
 export const wsUrl = url.replace('http://', 'ws://').replace('https://', 'wss://') + '/streaming';
-export const lang = miLocalStorage.getItem('lang');
+export const lang = miLocalStorage.getItem('lang') ?? 'en-US';
 export const langs = _LANGS_;
-export let locale = JSON.parse(miLocalStorage.getItem('locale'));
+const preParseLocale = miLocalStorage.getItem('locale');
+export let locale = preParseLocale ? JSON.parse(preParseLocale) : null;
 export const version = _VERSION_;
 export const instanceName = siteName === 'Misskey' ? host : siteName;
 export const ui = miLocalStorage.getItem('ui');
 export const debug = miLocalStorage.getItem('debug') === 'true';
 
-export function updateLocale(newLocale) {
+export function updateLocale(newLocale): void {
 	locale = newLocale;
 }
diff --git a/packages/frontend/src/init.ts b/packages/frontend/src/init.ts
index 5b3e7ec932..91cdc15ef9 100644
--- a/packages/frontend/src/init.ts
+++ b/packages/frontend/src/init.ts
@@ -6,18 +6,6 @@ import 'vite/modulepreload-polyfill';
 
 import '@/style.scss';
 
-//#region account indexedDB migration
-import { set } from '@/scripts/idb-proxy';
-
-{
-	const accounts = miLocalStorage.getItem('accounts');
-	if (accounts) {
-		set('accounts', JSON.parse(accounts));
-		miLocalStorage.removeItem('accounts');
-	}
-}
-//#endregion
-
 import { computed, createApp, watch, markRaw, version as vueVersion, defineAsyncComponent } from 'vue';
 import { compareVersions } from 'compare-versions';
 import JSON5 from 'json5';
@@ -42,11 +30,11 @@ import { reloadChannel } from '@/scripts/unison-reload';
 import { reactionPicker } from '@/scripts/reaction-picker';
 import { getUrlWithoutLoginId } from '@/scripts/login-id';
 import { getAccountFromId } from '@/scripts/get-account-from-id';
-import { deckStore } from './ui/deck/deck-store';
-import { miLocalStorage } from './local-storage';
-import { claimAchievement, claimedAchievements } from './scripts/achievements';
-import { fetchCustomEmojis } from './custom-emojis';
-import { mainRouter } from './router';
+import { deckStore } from '@/ui/deck/deck-store';
+import { miLocalStorage } from '@/local-storage';
+import { claimAchievement, claimedAchievements } from '@/scripts/achievements';
+import { fetchCustomEmojis } from '@/custom-emojis';
+import { mainRouter } from '@/router';
 
 console.info(`Misskey v${version}`);
 
@@ -55,7 +43,9 @@ if (_DEV_) {
 
 	console.info(`vue ${vueVersion}`);
 
+	// eslint-disable-next-line @typescript-eslint/no-explicit-any
 	(window as any).$i = $i;
+	// eslint-disable-next-line @typescript-eslint/no-explicit-any
 	(window as any).$store = defaultStore;
 
 	window.addEventListener('error', event => {
@@ -184,7 +174,7 @@ fetchInstanceMetaPromise.then(() => {
 
 try {
 	await fetchCustomEmojis();
-} catch (err) {}
+} catch (err) { /* empty */ }
 
 const app = createApp(
 	new URLSearchParams(window.location.search).has('zen') ? defineAsyncComponent(() => import('@/ui/zen.vue')) :
@@ -212,20 +202,20 @@ await deckStore.ready;
 
 // https://github.com/misskey-dev/misskey/pull/8575#issuecomment-1114239210
 // なぜかinit.tsの内容が2回実行されることがあるため、mountするdivを1つに制限する
-const rootEl = (() => {
+const rootEl = ((): HTMLElement => {
 	const MISSKEY_MOUNT_DIV_ID = 'misskey_app';
 
-	const currentEl = document.getElementById(MISSKEY_MOUNT_DIV_ID);
+	const currentRoot = document.getElementById(MISSKEY_MOUNT_DIV_ID);
 
-	if (currentEl) {
+	if (currentRoot) {
 		console.warn('multiple import detected');
-		return currentEl;
+		return currentRoot;
 	}
 
-	const rootEl = document.createElement('div');
-	rootEl.id = MISSKEY_MOUNT_DIV_ID;
-	document.body.appendChild(rootEl);
-	return rootEl;
+	const root = document.createElement('div');
+	root.id = MISSKEY_MOUNT_DIV_ID;
+	document.body.appendChild(root);
+	return root;
 })();
 
 app.mount(rootEl);
@@ -256,8 +246,7 @@ if (lastVersion !== version) {
 				popup(defineAsyncComponent(() => import('@/components/MkUpdated.vue')), {}, {}, 'closed');
 			}
 		}
-	} catch (err) {
-	}
+	} catch (err) { /* empty */ }
 }
 
 await defaultStore.ready;
diff --git a/packages/frontend/src/local-storage.ts b/packages/frontend/src/local-storage.ts
index 9a288f264c..441a35747a 100644
--- a/packages/frontend/src/local-storage.ts
+++ b/packages/frontend/src/local-storage.ts
@@ -24,6 +24,7 @@ type Keys =
 	'customCss' |
 	'message_drafts' |
 	'scratchpad' |
+	'debug' |
 	`miux:${string}` |
 	`ui:folder:${string}` |
 	`themes:${string}` |
@@ -32,7 +33,7 @@ type Keys =
 	'emojis' // DEPRECATED, stored in indexeddb (13.9.0~);
 
 export const miLocalStorage = {
-	getItem: (key: Keys) => window.localStorage.getItem(key),
-	setItem: (key: Keys, value: string) => window.localStorage.setItem(key, value),
-	removeItem: (key: Keys) => window.localStorage.removeItem(key),
+	getItem: (key: Keys): string | null => window.localStorage.getItem(key),
+	setItem: (key: Keys, value: string): void => window.localStorage.setItem(key, value),
+	removeItem: (key: Keys): void => window.localStorage.removeItem(key),
 };