diff --git a/packages/backend/src/models/json-schema/notification.ts b/packages/backend/src/models/json-schema/notification.ts
index 6f5fb8247b..b05ec8b762 100644
--- a/packages/backend/src/models/json-schema/notification.ts
+++ b/packages/backend/src/models/json-schema/notification.ts
@@ -3,6 +3,7 @@
  * SPDX-License-Identifier: AGPL-3.0-only
  */
 
+import { ACHIEVEMENT_TYPES } from '@/core/AchievementService.js';
 import { notificationTypes } from '@/types.js';
 
 const baseSchema = {
@@ -294,6 +295,7 @@ export const packedNotificationSchema = {
 			achievement: {
 				type: 'string',
 				optional: false, nullable: false,
+				enum: ACHIEVEMENT_TYPES,
 			},
 		},
 	}, {
diff --git a/packages/frontend/src/scripts/i18n.ts b/packages/frontend/src/scripts/i18n.ts
index c2f44a33cc..b258a2a678 100644
--- a/packages/frontend/src/scripts/i18n.ts
+++ b/packages/frontend/src/scripts/i18n.ts
@@ -137,7 +137,6 @@ export class I18n<T extends ILocale> {
 			return this.tsxCache = new Proxy(this.locale, new Handler()) as unknown as Tsx<T>;
 		}
 
-		// eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
 		if (this.tsxCache) {
 			return this.tsxCache;
 		}
@@ -244,51 +243,3 @@ export class I18n<T extends ILocale> {
 		return str;
 	}
 }
-
-if (import.meta.vitest) {
-	const { describe, expect, it } = import.meta.vitest;
-
-	describe('i18n', () => {
-		it('t', () => {
-			const i18n = new I18n({
-				foo: 'foo',
-				bar: {
-					baz: 'baz',
-					qux: 'qux {0}' as unknown as ParameterizedString<'0'>,
-					quux: 'quux {0} {1}' as unknown as ParameterizedString<'0' | '1'>,
-				},
-			});
-
-			expect(i18n.t('foo')).toBe('foo');
-			expect(i18n.t('bar.baz')).toBe('baz');
-			expect(i18n.tsx.bar.qux({ 0: 'hoge' })).toBe('qux hoge');
-			expect(i18n.tsx.bar.quux({ 0: 'hoge', 1: 'fuga' })).toBe('quux hoge fuga');
-		});
-		it('ts', () => {
-			const i18n = new I18n({
-				foo: 'foo',
-				bar: {
-					baz: 'baz',
-					qux: 'qux {0}' as unknown as ParameterizedString<'0'>,
-					quux: 'quux {0} {1}' as unknown as ParameterizedString<'0' | '1'>,
-				},
-			});
-
-			expect(i18n.ts.foo).toBe('foo');
-			expect(i18n.ts.bar.baz).toBe('baz');
-		});
-		it('tsx', () => {
-			const i18n = new I18n({
-				foo: 'foo',
-				bar: {
-					baz: 'baz',
-					qux: 'qux {0}' as unknown as ParameterizedString<'0'>,
-					quux: 'quux {0} {1}' as unknown as ParameterizedString<'0' | '1'>,
-				},
-			});
-
-			expect(i18n.tsx.bar.qux({ 0: 'hoge' })).toBe('qux hoge');
-			expect(i18n.tsx.bar.quux({ 0: 'hoge', 1: 'fuga' })).toBe('quux hoge fuga');
-		});
-	});
-}
diff --git a/packages/frontend/test/i18n.test.ts b/packages/frontend/test/i18n.test.ts
new file mode 100644
index 0000000000..e1cab1f15f
--- /dev/null
+++ b/packages/frontend/test/i18n.test.ts
@@ -0,0 +1,52 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { describe, expect, it } from 'vitest';
+import { I18n } from '@/scripts/i18n.js';
+import { ParameterizedString } from '../../../locales/index.js';
+
+describe('i18n', () => {
+	it('t', () => {
+		const i18n = new I18n({
+			foo: 'foo',
+			bar: {
+				baz: 'baz',
+				qux: 'qux {0}' as unknown as ParameterizedString<'0'>,
+				quux: 'quux {0} {1}' as unknown as ParameterizedString<'0' | '1'>,
+			},
+		});
+
+		expect(i18n.t('foo')).toBe('foo');
+		expect(i18n.t('bar.baz')).toBe('baz');
+		expect(i18n.tsx.bar.qux({ 0: 'hoge' })).toBe('qux hoge');
+		expect(i18n.tsx.bar.quux({ 0: 'hoge', 1: 'fuga' })).toBe('quux hoge fuga');
+	});
+	it('ts', () => {
+		const i18n = new I18n({
+			foo: 'foo',
+			bar: {
+				baz: 'baz',
+				qux: 'qux {0}' as unknown as ParameterizedString<'0'>,
+				quux: 'quux {0} {1}' as unknown as ParameterizedString<'0' | '1'>,
+			},
+		});
+
+		expect(i18n.ts.foo).toBe('foo');
+		expect(i18n.ts.bar.baz).toBe('baz');
+	});
+	it('tsx', () => {
+		const i18n = new I18n({
+			foo: 'foo',
+			bar: {
+				baz: 'baz',
+				qux: 'qux {0}' as unknown as ParameterizedString<'0'>,
+				quux: 'quux {0} {1}' as unknown as ParameterizedString<'0' | '1'>,
+			},
+		});
+
+		expect(i18n.tsx.bar.qux({ 0: 'hoge' })).toBe('qux hoge');
+		expect(i18n.tsx.bar.quux({ 0: 'hoge', 1: 'fuga' })).toBe('quux hoge fuga');
+	});
+});
diff --git a/packages/misskey-js/src/autogen/types.ts b/packages/misskey-js/src/autogen/types.ts
index 3f866a9ab3..37f1bf2d38 100644
--- a/packages/misskey-js/src/autogen/types.ts
+++ b/packages/misskey-js/src/autogen/types.ts
@@ -4245,15 +4245,16 @@ export type components = {
       /** @enum {string} */
       type: 'roleAssigned';
       role: components['schemas']['Role'];
-    } | {
+    } | ({
       /** Format: id */
       id: string;
       /** Format: date-time */
       createdAt: string;
       /** @enum {string} */
       type: 'achievementEarned';
-      achievement: string;
-    } | ({
+      /** @enum {string} */
+      achievement: 'notes1' | 'notes10' | 'notes100' | 'notes500' | 'notes1000' | 'notes5000' | 'notes10000' | 'notes20000' | 'notes30000' | 'notes40000' | 'notes50000' | 'notes60000' | 'notes70000' | 'notes80000' | 'notes90000' | 'notes100000' | 'login3' | 'login7' | 'login15' | 'login30' | 'login60' | 'login100' | 'login200' | 'login300' | 'login400' | 'login500' | 'login600' | 'login700' | 'login800' | 'login900' | 'login1000' | 'passedSinceAccountCreated1' | 'passedSinceAccountCreated2' | 'passedSinceAccountCreated3' | 'loggedInOnBirthday' | 'loggedInOnNewYearsDay' | 'noteClipped1' | 'noteFavorited1' | 'myNoteFavorited1' | 'profileFilled' | 'markedAsCat' | 'following1' | 'following10' | 'following50' | 'following100' | 'following300' | 'followers1' | 'followers10' | 'followers50' | 'followers100' | 'followers300' | 'followers500' | 'followers1000' | 'collectAchievements30' | 'viewAchievements3min' | 'iLoveMisskey' | 'foundTreasure' | 'client30min' | 'client60min' | 'noteDeletedWithin1min' | 'postedAtLateNight' | 'postedAt0min0sec' | 'selfQuote' | 'htl20npm' | 'viewInstanceChart' | 'outputHelloWorldOnScratchpad' | 'open3windows' | 'driveFolderCircularReference' | 'reactWithoutRead' | 'clickedClickHere' | 'justPlainLucky' | 'setNameToSyuilo' | 'cookieClicked' | 'brainDiver' | 'smashTestNotificationButton' | 'tutorialCompleted' | 'bubbleGameExplodingHead' | 'bubbleGameDoubleExplodingHead';
+    }) | ({
       /** Format: id */
       id: string;
       /** Format: date-time */
diff --git a/packages/sw/src/scripts/create-notification.ts b/packages/sw/src/scripts/create-notification.ts
index 7d28d8a694..02d9b07767 100644
--- a/packages/sw/src/scripts/create-notification.ts
+++ b/packages/sw/src/scripts/create-notification.ts
@@ -41,11 +41,10 @@ export async function createNotification<K extends keyof PushNotificationDataMap
 
 async function composeNotification(data: PushNotificationDataMap[keyof PushNotificationDataMap]): Promise<[string, NotificationOptions] | null> {
 	const i18n = await (swLang.i18n ?? swLang.fetchLocale());
-	const { t } = i18n;
 	switch (data.type) {
 		/*
 		case 'driveFileCreated': // TODO (Server Side)
-			return [t('_notification.fileUploaded'), {
+			return [i18n.ts._notification.fileUploaded, {
 				body: body.name,
 				icon: body.url,
 				data
@@ -58,7 +57,7 @@ async function composeNotification(data: PushNotificationDataMap[keyof PushNotif
 					const account = await getAccountFromId(data.userId);
 					if (!account) return null;
 					const userDetail = await cli.request('users/show', { userId: data.body.userId }, account.token);
-					return [t('_notification.youWereFollowed'), {
+					return [i18n.ts._notification.youWereFollowed, {
 						body: getUserName(data.body.user),
 						icon: data.body.user.avatarUrl,
 						badge: iconUrl('user-plus'),
@@ -66,14 +65,14 @@ async function composeNotification(data: PushNotificationDataMap[keyof PushNotif
 						actions: userDetail.isFollowing ? [] : [
 							{
 								action: 'follow',
-								title: t('_notification._actions.followBack'),
+								title: i18n.ts._notification._actions.followBack,
 							},
 						],
 					}];
 				}
 
 				case 'mention':
-					return [t('_notification.youGotMention', { name: getUserName(data.body.user) }), {
+					return [i18n.tsx._notification.youGotMention({ name: getUserName(data.body.user) }), {
 						body: data.body.note.text ?? '',
 						icon: data.body.user.avatarUrl,
 						badge: iconUrl('at'),
@@ -81,13 +80,13 @@ async function composeNotification(data: PushNotificationDataMap[keyof PushNotif
 						actions: [
 							{
 								action: 'reply',
-								title: t('_notification._actions.reply'),
+								title: i18n.ts._notification._actions.reply,
 							},
 						],
 					}];
 
 				case 'reply':
-					return [t('_notification.youGotReply', { name: getUserName(data.body.user) }), {
+					return [i18n.tsx._notification.youGotReply({ name: getUserName(data.body.user) }), {
 						body: data.body.note.text ?? '',
 						icon: data.body.user.avatarUrl,
 						badge: iconUrl('arrow-back-up'),
@@ -95,13 +94,13 @@ async function composeNotification(data: PushNotificationDataMap[keyof PushNotif
 						actions: [
 							{
 								action: 'reply',
-								title: t('_notification._actions.reply'),
+								title: i18n.ts._notification._actions.reply,
 							},
 						],
 					}];
 
 				case 'renote':
-					return [t('_notification.youRenoted', { name: getUserName(data.body.user) }), {
+					return [i18n.tsx._notification.youRenoted({ name: getUserName(data.body.user) }), {
 						body: data.body.note.text ?? '',
 						icon: data.body.user.avatarUrl,
 						badge: iconUrl('repeat'),
@@ -115,7 +114,7 @@ async function composeNotification(data: PushNotificationDataMap[keyof PushNotif
 					}];
 
 				case 'quote':
-					return [t('_notification.youGotQuote', { name: getUserName(data.body.user) }), {
+					return [i18n.tsx._notification.youGotQuote({ name: getUserName(data.body.user) }), {
 						body: data.body.note.text ?? '',
 						icon: data.body.user.avatarUrl,
 						badge: iconUrl('quote'),
@@ -123,19 +122,19 @@ async function composeNotification(data: PushNotificationDataMap[keyof PushNotif
 						actions: [
 							{
 								action: 'reply',
-								title: t('_notification._actions.reply'),
+								title: i18n.ts._notification._actions.reply,
 							},
 							...((data.body.note.visibility === 'public' || data.body.note.visibility === 'home') ? [
 								{
 									action: 'renote',
-									title: t('_notification._actions.renote'),
+									title: i18n.ts._notification._actions.renote,
 								},
 							] : []),
 						],
 					}];
 
 				case 'note':
-					return [t('_notification.newNote') + ': ' + getUserName(data.body.user), {
+					return [i18n.ts._notification.newNote + ': ' + getUserName(data.body.user), {
 						body: data.body.note.text ?? '',
 						icon: data.body.user.avatarUrl,
 						data,
@@ -178,7 +177,7 @@ async function composeNotification(data: PushNotificationDataMap[keyof PushNotif
 				}
 
 				case 'receiveFollowRequest':
-					return [t('_notification.youReceivedFollowRequest'), {
+					return [i18n.ts._notification.youReceivedFollowRequest, {
 						body: getUserName(data.body.user),
 						icon: data.body.user.avatarUrl,
 						badge: iconUrl('user-plus'),
@@ -186,17 +185,17 @@ async function composeNotification(data: PushNotificationDataMap[keyof PushNotif
 						actions: [
 							{
 								action: 'accept',
-								title: t('accept'),
+								title: i18n.ts.accept,
 							},
 							{
 								action: 'reject',
-								title: t('reject'),
+								title: i18n.ts.reject,
 							},
 						],
 					}];
 
 				case 'followRequestAccepted':
-					return [t('_notification.yourFollowRequestAccepted'), {
+					return [i18n.ts._notification.yourFollowRequestAccepted, {
 						body: getUserName(data.body.user),
 						icon: data.body.user.avatarUrl,
 						badge: iconUrl('circle-check'),
@@ -204,15 +203,15 @@ async function composeNotification(data: PushNotificationDataMap[keyof PushNotif
 					}];
 
 				case 'achievementEarned':
-					return [t('_notification.achievementEarned'), {
-						body: t(`_achievements._types._${data.body.achievement}.title`),
+					return [i18n.ts._notification.achievementEarned, {
+						body: i18n.ts._achievements._types[`_${data.body.achievement}`].title,
 						badge: iconUrl('medal'),
 						data,
 						tag: `achievement:${data.body.achievement}`,
 					}];
 
 				case 'pollEnded':
-					return [t('_notification.pollEnded'), {
+					return [i18n.ts._notification.pollEnded, {
 						body: data.body.note.text ?? '',
 						badge: iconUrl('chart-arrows'),
 						data,
@@ -226,8 +225,8 @@ async function composeNotification(data: PushNotificationDataMap[keyof PushNotif
 					}];
 
 				case 'test':
-					return [t('_notification.testNotification'), {
-						body: t('_notification.notificationWillBeDisplayedLikeThis'),
+					return [i18n.ts._notification.testNotification, {
+						body: i18n.ts._notification.notificationWillBeDisplayedLikeThis,
 						badge: iconUrl('bell'),
 						data,
 					}];
@@ -236,7 +235,7 @@ async function composeNotification(data: PushNotificationDataMap[keyof PushNotif
 					return null;
 			}
 		case 'unreadAntennaNote':
-			return [t('_notification.unreadAntennaNote', { name: data.body.antenna.name }), {
+			return [i18n.tsx._notification.unreadAntennaNote({ name: data.body.antenna.name }), {
 				body: `${getUserName(data.body.note.user)}: ${data.body.note.text ?? ''}`,
 				icon: data.body.note.user.avatarUrl,
 				badge: iconUrl('antenna'),
@@ -252,7 +251,6 @@ async function composeNotification(data: PushNotificationDataMap[keyof PushNotif
 export async function createEmptyNotification(): Promise<void> {
 	return new Promise<void>(async res => {
 		const i18n = await (swLang.i18n ?? swLang.fetchLocale());
-		const { t } = i18n;
 
 		await globalThis.registration.showNotification(
 			(new URL(origin)).host,
@@ -264,11 +262,11 @@ export async function createEmptyNotification(): Promise<void> {
 				actions: [
 					{
 						action: 'markAllAsRead',
-						title: t('markAllAsRead'),
+						title: i18n.ts.markAllAsRead,
 					},
 					{
 						action: 'settings',
-						title: t('notificationSettings'),
+						title: i18n.ts.notificationSettings,
 					},
 				],
 				data: {},
diff --git a/packages/sw/src/scripts/i18n.ts b/packages/sw/src/scripts/i18n.ts
deleted file mode 100644
index 77b955dbe8..0000000000
--- a/packages/sw/src/scripts/i18n.ts
+++ /dev/null
@@ -1,37 +0,0 @@
-/*
- * SPDX-FileCopyrightText: syuilo and misskey-project
- * SPDX-License-Identifier: AGPL-3.0-only
- */
-
-export type Locale = { [key: string]: string | Locale };
-
-export class I18n<T extends Locale = Locale> {
-	public ts: T;
-
-	constructor(locale: T) {
-		this.ts = locale;
-
-		//#region BIND
-		this.t = this.t.bind(this);
-		//#endregion
-	}
-
-	// string にしているのは、ドット区切りでのパス指定を許可するため
-	// なるべくこのメソッド使うよりもlocale直接参照の方がvueのキャッシュ効いてパフォーマンスが良いかも
-	public t(key: string, args?: Record<string, string>): string {
-		try {
-			let str = key.split('.').reduce<Locale | Locale[keyof Locale]>((o, i) => o[i], this.ts);
-			if (typeof str !== 'string') throw new Error();
-
-			if (args) {
-				for (const [k, v] of Object.entries(args)) {
-					str = str.replace(`{${k}}`, v);
-				}
-			}
-			return str;
-		} catch (err) {
-			console.warn(`missing localization '${key}'`);
-			return key;
-		}
-	}
-}
diff --git a/packages/sw/src/scripts/lang.ts b/packages/sw/src/scripts/lang.ts
index 6fccedd746..0db4cc6381 100644
--- a/packages/sw/src/scripts/lang.ts
+++ b/packages/sw/src/scripts/lang.ts
@@ -7,7 +7,8 @@
  * Language manager for SW
  */
 import { get, set } from 'idb-keyval';
-import { I18n, type Locale } from '@/scripts/i18n.js';
+import { I18n } from '../../../frontend/src/scripts/i18n.js';
+import type { Locale } from '../../../../locales/index.js';
 
 class SwLang {
 	public cacheName = `mk-cache-${_VERSION_}`;
@@ -23,7 +24,7 @@ class SwLang {
 		return this.fetchLocale();
 	}
 
-	public i18n: Promise<I18n> | null = null;
+	public i18n: Promise<I18n<Locale>> | null = null;
 
 	public fetchLocale(): Promise<I18n<Locale>> {
 		return (this.i18n = this._fetch());
diff --git a/packages/sw/src/sw.ts b/packages/sw/src/sw.ts
index cc79d88713..7a0010992e 100644
--- a/packages/sw/src/sw.ts
+++ b/packages/sw/src/sw.ts
@@ -6,7 +6,8 @@
 import { get } from 'idb-keyval';
 import * as Misskey from 'misskey-js';
 import type { PushNotificationDataMap } from '@/types.js';
-import type { I18n, Locale } from '@/scripts/i18n.js';
+import type { I18n } from '../../frontend/src/scripts/i18n.js';
+import type { Locale } from '../../../locales/index.js';
 import { createEmptyNotification, createNotification } from '@/scripts/create-notification.js';
 import { swLang } from '@/scripts/lang.js';
 import * as swos from '@/scripts/operations.js';
@@ -30,8 +31,8 @@ globalThis.addEventListener('activate', ev => {
 async function offlineContentHTML() {
 	const i18n = await (swLang.i18n ?? swLang.fetchLocale()) as Partial<I18n<Locale>>;
 	const messages = {
-		title: i18n.ts?._offlineScreen?.title ?? 'Offline - Could not connect to server',
-		header: i18n.ts?._offlineScreen?.header ?? 'Could not connect to server',
+		title: i18n.ts?._offlineScreen.title ?? 'Offline - Could not connect to server',
+		header: i18n.ts?._offlineScreen.header ?? 'Could not connect to server',
 		reload: i18n.ts?.reload ?? 'Reload',
 	};