diff --git a/.changeset/cjk-slide-ids.md b/.changeset/cjk-slide-ids.md
new file mode 100644
index 000000000..0e67980fe
--- /dev/null
+++ b/.changeset/cjk-slide-ids.md
@@ -0,0 +1,5 @@
+---
+'@open-slide/core': patch
+---
+
+Accept Unicode (including CJK) slide folder ids for discovery and mutations.
diff --git a/packages/core/src/app/lib/assets.ts b/packages/core/src/app/lib/assets.ts
index 17c9dacda..cc37f32bc 100644
--- a/packages/core/src/app/lib/assets.ts
+++ b/packages/core/src/app/lib/assets.ts
@@ -12,9 +12,15 @@ export type AssetEntry = {
 
 export type UploadOptions = { overwrite?: boolean };
 
+function assetsScopeUrl(slideId: string, ...parts: string[]): string {
+  const segments = [encodeURIComponent(slideId), ...parts.map((p) => encodeURIComponent(p))];
+  return `/__assets/${segments.join('/')}`;
+}
+
 export async function listAssets(slideId: string): Promise<AssetEntry[]> {
-  const res = await fetch(`/__assets/${slideId}`);
-  if (!res.ok) throw new Error(`GET /__assets/${slideId} ${res.status}`);
+  const url = assetsScopeUrl(slideId);
+  const res = await fetch(url);
+  if (!res.ok) throw new Error(`GET ${url} ${res.status}`);
   const data = (await res.json()) as { assets?: AssetEntry[] };
   return data.assets ?? [];
 }
@@ -25,7 +31,7 @@ export async function uploadAsset(
   opts: UploadOptions = {},
 ): Promise<Response> {
   const qs = opts.overwrite ? '?overwrite=1' : '';
-  return fetch(`/__assets/${slideId}/${encodeURIComponent(file.name)}${qs}`, {
+  return fetch(`${assetsScopeUrl(slideId, file.name)}${qs}`, {
     method: 'POST',
     headers: {
       'content-type': file.type || 'application/octet-stream',
@@ -36,7 +42,7 @@ export async function uploadAsset(
 }
 
 async function renameAsset(slideId: string, from: string, to: string): Promise<Response> {
-  return fetch(`/__assets/${slideId}/${encodeURIComponent(from)}`, {
+  return fetch(assetsScopeUrl(slideId, from), {
     method: 'PATCH',
     headers: { 'content-type': 'application/json' },
     body: JSON.stringify({ name: to }),
@@ -44,13 +50,13 @@ async function renameAsset(slideId: string, from: string, to: string): Promise<R
 }
 
 async function deleteAsset(slideId: string, name: string): Promise<Response> {
-  return fetch(`/__assets/${slideId}/${encodeURIComponent(name)}`, { method: 'DELETE' });
+  return fetch(assetsScopeUrl(slideId, name), { method: 'DELETE' });
 }
 
 export type AssetUsage = { slideId: string; count: number };
 
 export async function listAssetUsages(slideId: string, name: string): Promise<AssetUsage[]> {
-  const res = await fetch(`/__assets/${slideId}/${encodeURIComponent(name)}/usages`);
+  const res = await fetch(`${assetsScopeUrl(slideId, name)}/usages`);
   if (!res.ok) return [];
   const data = (await res.json().catch(() => null)) as { usages?: AssetUsage[] } | null;
   return data?.usages ?? [];
@@ -93,7 +99,7 @@ export async function uploadWithAutoRename(
     createdAt: body?.createdAt ?? now,
     mtime: body?.mtime ?? now,
     mime: body?.mime ?? uploaded.type ?? 'application/octet-stream',
-    url: body?.url ?? `/__assets/${slideId}/${encodeURIComponent(uploaded.name)}`,
+    url: body?.url ?? assetsScopeUrl(slideId, uploaded.name),
     unused: body?.unused ?? false,
   };
   return { ok: true, status: res.status, entry };
diff --git a/packages/core/src/app/lib/folders.ts b/packages/core/src/app/lib/folders.ts
index dc636220f..229cc1a6e 100644
--- a/packages/core/src/app/lib/folders.ts
+++ b/packages/core/src/app/lib/folders.ts
@@ -25,30 +25,33 @@ async function getManifest(): Promise<FoldersManifest> {
 }
 
 async function patchSlideName(slideId: string, name: string): Promise<void> {
-  const res = await fetch(`/__slides/${slideId}`, {
+  const id = encodeURIComponent(slideId);
+  const res = await fetch(`/__slides/${id}`, {
     method: 'PATCH',
     headers: { 'content-type': 'application/json' },
     body: JSON.stringify({ name }),
   });
-  if (!res.ok) throw new Error(`PATCH /__slides/${slideId} ${res.status}`);
+  if (!res.ok) throw new Error(`PATCH /__slides/${id} ${res.status}`);
 }
 
 async function duplicateSlideReq(slideId: string, newId?: string): Promise<string> {
+  const id = encodeURIComponent(slideId);
   const init: RequestInit = { method: 'POST' };
   if (newId !== undefined) {
     init.headers = { 'content-type': 'application/json' };
     init.body = JSON.stringify({ newId });
   }
-  const res = await fetch(`/__slides/${slideId}/duplicate`, init);
-  if (!res.ok) throw new Error(`POST /__slides/${slideId}/duplicate ${res.status}`);
+  const res = await fetch(`/__slides/${id}/duplicate`, init);
+  if (!res.ok) throw new Error(`POST /__slides/${id}/duplicate ${res.status}`);
   const body = (await res.json()) as { slideId?: unknown };
   if (typeof body.slideId !== 'string') throw new Error('duplicate response missing slideId');
   return body.slideId;
 }
 
 async function deleteSlideReq(slideId: string): Promise<void> {
-  const res = await fetch(`/__slides/${slideId}`, { method: 'DELETE' });
-  if (!res.ok) throw new Error(`DELETE /__slides/${slideId} ${res.status}`);
+  const id = encodeURIComponent(slideId);
+  const res = await fetch(`/__slides/${id}`, { method: 'DELETE' });
+  if (!res.ok) throw new Error(`DELETE /__slides/${id} ${res.status}`);
 }
 
 async function postFolder(name: string, icon: FolderIcon): Promise<Folder> {
diff --git a/packages/core/src/editing/slide-ops.test.ts b/packages/core/src/editing/slide-ops.test.ts
index a3b5c552c..7f123dfb3 100644
--- a/packages/core/src/editing/slide-ops.test.ts
+++ b/packages/core/src/editing/slide-ops.test.ts
@@ -10,6 +10,9 @@ import {
   removePageFromDefaultExportInSource,
   reorderDefaultExportPagesInSource,
   reorderNotesArrayInSource,
+  resolveSlideEntry,
+  rmSlideDir,
+  SLIDE_ID_RE,
   updateMetaTitleInSource,
   validateSlideName,
 } from './slide-ops.ts';
@@ -33,6 +36,35 @@ async function writeSlide(root: string, id: string, title = id): Promise<void> {
   await fs.writeFile(path.join(root, id, 'assets', 'hero.txt'), 'hero', 'utf8');
 }
 
+describe('SLIDE_ID_RE', () => {
+  it('accepts ASCII kebab ids and CJK letter ids', () => {
+    expect(SLIDE_ID_RE.test('cover')).toBe(true);
+    expect(SLIDE_ID_RE.test('intro_2')).toBe(true);
+    expect(SLIDE_ID_RE.test('推薦系統')).toBe(true);
+    expect(SLIDE_ID_RE.test('簡報-v2')).toBe(true);
+  });
+
+  it('rejects spaces, dots, and path separators', () => {
+    expect(SLIDE_ID_RE.test('bad id')).toBe(false);
+    expect(SLIDE_ID_RE.test('has.dot')).toBe(false);
+    expect(SLIDE_ID_RE.test('../escape')).toBe(false);
+    expect(SLIDE_ID_RE.test('a/b')).toBe(false);
+  });
+});
+
+describe('resolveSlideEntry / rmSlideDir with CJK ids', () => {
+  it('resolves and removes a CJK slide directory', async () => {
+    await withSlidesRoot(async (root) => {
+      await writeSlide(root, '推薦系統');
+      expect(resolveSlideEntry(root, '推薦系統')).toBe(path.join(root, '推薦系統', 'index.tsx'));
+      expect(await rmSlideDir(root, '推薦系統')).toBe(true);
+      await expect(fs.access(path.join(root, '推薦系統'))).rejects.toMatchObject({
+        code: 'ENOENT',
+      });
+    });
+  });
+});
+
 describe('duplicateSlideDir', () => {
   it('duplicates a slide directory with an automatic copy id', async () => {
     await withSlidesRoot(async (root) => {
@@ -68,6 +100,25 @@ describe('duplicateSlideDir', () => {
     });
   });
 
+  it('duplicates a CJK slide id and accepts a CJK desired id', async () => {
+    await withSlidesRoot(async (root) => {
+      await writeSlide(root, '推薦系統', '推薦系統');
+
+      expect(await duplicateSlideDir(root, '推薦系統')).toEqual({
+        ok: true,
+        slideId: '推薦系統-copy',
+      });
+      expect(await duplicateSlideDir(root, '推薦系統', '複本簡報')).toEqual({
+        ok: true,
+        slideId: '複本簡報',
+      });
+      await expect(
+        fs.access(path.join(root, '推薦系統-copy', 'index.tsx')),
+      ).resolves.toBeUndefined();
+      await expect(fs.access(path.join(root, '複本簡報', 'index.tsx'))).resolves.toBeUndefined();
+    });
+  });
+
   it('rejects an existing desired id', async () => {
     await withSlidesRoot(async (root) => {
       await writeSlide(root, 'cover');
diff --git a/packages/core/src/editing/slide-ops.ts b/packages/core/src/editing/slide-ops.ts
index b040d0161..84d2f1015 100644
--- a/packages/core/src/editing/slide-ops.ts
+++ b/packages/core/src/editing/slide-ops.ts
@@ -2,7 +2,11 @@ import fs from 'node:fs/promises';
 import path from 'node:path';
 import { parse as babelParse } from '@babel/parser';
 
-export const SLIDE_ID_RE = /^[a-z0-9_-]+$/i;
+// Letters (any script, including CJK) + digits + hyphen/underscore. Rejects
+// spaces, dots, path separators, and other punctuation so ids stay safe for
+// filesystem joins and `/__slides/:id` URL segments. Path traversal is still
+// blocked by the resolve+prefix checks below.
+export const SLIDE_ID_RE = /^[\p{L}\p{N}_-]+$/u;
 
 type MetaTitleRead =
   | { kind: 'found'; title: string }
diff --git a/packages/core/src/vite/open-slide-plugin.test.ts b/packages/core/src/vite/open-slide-plugin.test.ts
index 43311d479..17a5a6fff 100644
--- a/packages/core/src/vite/open-slide-plugin.test.ts
+++ b/packages/core/src/vite/open-slide-plugin.test.ts
@@ -36,15 +36,27 @@ describe('generateSlidesModule', () => {
     });
   });
 
-  it('excludes folders whose id is not ASCII-safe and reports them as ignored', async () => {
+  it('keeps CJK slide ids and lists them alongside ASCII ids', async () => {
     await withSlidesRoot(async (root) => {
       const files = [await writeSlide(root, 'cover'), await writeSlide(root, '推薦系統')].sort();
 
       const { code, ignored } = await generateSlidesModule(files, root, false);
 
-      expect(ignored).toEqual(['推薦系統']);
+      expect(ignored).toEqual([]);
+      expect(code).toContain('export const slideIds = ["cover","推薦系統"];');
+      expect(code).toContain('推薦系統');
+    });
+  });
+
+  it('excludes folders whose id has spaces or punctuation and reports them as ignored', async () => {
+    await withSlidesRoot(async (root) => {
+      const files = [await writeSlide(root, 'cover'), await writeSlide(root, 'bad id')].sort();
+
+      const { code, ignored } = await generateSlidesModule(files, root, false);
+
+      expect(ignored).toEqual(['bad id']);
       expect(code).toContain('export const slideIds = ["cover"];');
-      expect(code).not.toContain('推薦系統');
+      expect(code).not.toContain('bad id');
     });
   });
 });
diff --git a/packages/core/src/vite/open-slide-plugin.ts b/packages/core/src/vite/open-slide-plugin.ts
index 661e04dc7..265cdeb8c 100644
--- a/packages/core/src/vite/open-slide-plugin.ts
+++ b/packages/core/src/vite/open-slide-plugin.ts
@@ -135,9 +135,10 @@ export async function generateSlidesModule(
   );
 
   // Discovery globs every `slides/*/index.*`, but a slide id is used in URLs,
-  // filesystem paths, and the editing routes — all guarded by SLIDE_ID_RE. Drop
-  // folders with an unusable id instead of listing them as slides that then fail
-  // every folder/edit action; `load` warns about each ignored folder.
+  // filesystem paths, and the editing routes — all guarded by SLIDE_ID_RE
+  // (Unicode letters/digits plus "-"/"_"). Drop folders with an unusable id
+  // instead of listing them as slides that then fail every folder/edit action;
+  // `load` warns about each ignored folder.
   const entries = scanned.filter((e) => SLIDE_ID_RE.test(e.id));
   const ignored = scanned.filter((e) => !SLIDE_ID_RE.test(e.id)).map((e) => e.id);
 
@@ -246,7 +247,7 @@ export function openSlidePlugin(opts: OpenSlidePluginOptions): Plugin {
           if (warnedInvalidSlideIds.has(slideId)) continue;
           warnedInvalidSlideIds.add(slideId);
           this.warn(
-            `Ignoring slide folder "${slideId}": slide ids must match ${SLIDE_ID_RE} (lowercase/uppercase letters, digits, "-", "_"). Rename the folder under "${slidesDir}/" to a kebab-case id so it appears in the browser and can be moved into folders.`,
+            `Ignoring slide folder "${slideId}": slide ids must match ${SLIDE_ID_RE} (Unicode letters/digits, "-", "_"; no spaces or punctuation). Rename the folder under "${slidesDir}/" so it appears in the browser and can be moved into folders.`,
           );
         }
         return code;
diff --git a/packages/core/src/vite/routes/assets.ts b/packages/core/src/vite/routes/assets.ts
index 86df04171..c65d9bc5a 100644
--- a/packages/core/src/vite/routes/assets.ts
+++ b/packages/core/src/vite/routes/assets.ts
@@ -13,7 +13,7 @@ import {
   validateAssetName,
 } from '../../files/assets.ts';
 import { validateMutationRequest } from '../../http/request-guard.ts';
-import { type ApiContext, json, readBody } from './context.ts';
+import { type ApiContext, decodePathSegment, json, readBody } from './context.ts';
 
 // GET    /__assets/:scope                     list assets in slide or @global
 // GET    /__assets/:scope/:file               serve raw asset bytes
@@ -33,9 +33,10 @@ export function registerAssetRoutes(server: ViteDevServer, ctx: ApiContext): voi
       const usagesMatch = url.pathname.match(/^\/([^/]+)\/([^/]+)\/usages$/);
 
       if (usagesMatch && method === 'GET') {
-        const scope = usagesMatch[1];
-        const filename = decodeURIComponent(usagesMatch[2]);
-        if (!validateAssetName(filename)) return json(res, 400, { error: 'invalid path' });
+        const scope = decodePathSegment(usagesMatch[1]);
+        const filename = decodePathSegment(usagesMatch[2]);
+        if (!scope || filename === null || !validateAssetName(filename))
+          return json(res, 400, { error: 'invalid path' });
 
         const isGlobal = scope === GLOBAL_SCOPE;
         const assetPath = isGlobal ? `@assets/${filename}` : `./assets/${filename}`;
@@ -76,7 +77,8 @@ export function registerAssetRoutes(server: ViteDevServer, ctx: ApiContext): voi
       }
 
       if (listMatch && method === 'GET') {
-        const slideId = listMatch[1];
+        const slideId = decodePathSegment(listMatch[1]);
+        if (!slideId) return json(res, 400, { error: 'invalid slideId' });
         const scopedDir = resolveScopedAssetsDir(ctx.slidesRoot, ctx.globalAssetsRoot, slideId);
         if (!scopedDir) return json(res, 400, { error: 'invalid slideId' });
 
@@ -109,7 +111,7 @@ export function registerAssetRoutes(server: ViteDevServer, ctx: ApiContext): voi
             createdAt: assetCreatedAt(stat.birthtimeMs, stat.mtimeMs),
             mtime: stat.mtimeMs,
             mime: mimeForFilename(name),
-            url: `/__assets/${slideId}/${encodeURIComponent(name)}`,
+            url: `/__assets/${encodeURIComponent(slideId)}/${encodeURIComponent(name)}`,
             unused: true,
           });
         }
@@ -152,8 +154,9 @@ export function registerAssetRoutes(server: ViteDevServer, ctx: ApiContext): voi
       }
 
       if (fileMatch) {
-        const slideId = fileMatch[1];
-        const filename = decodeURIComponent(fileMatch[2]);
+        const slideId = decodePathSegment(fileMatch[1]);
+        const filename = decodePathSegment(fileMatch[2]);
+        if (!slideId || filename === null) return json(res, 400, { error: 'invalid path' });
         const file = resolveScopedAssetFile(
           ctx.slidesRoot,
           ctx.globalAssetsRoot,
@@ -230,7 +233,7 @@ export function registerAssetRoutes(server: ViteDevServer, ctx: ApiContext): voi
             createdAt: assetCreatedAt(stat.birthtimeMs, stat.mtimeMs),
             mtime: stat.mtimeMs,
             mime: mimeForFilename(filename),
-            url: `/__assets/${slideId}/${encodeURIComponent(filename)}`,
+            url: `/__assets/${encodeURIComponent(slideId)}/${encodeURIComponent(filename)}`,
           });
         }
 
diff --git a/packages/core/src/vite/routes/context.test.ts b/packages/core/src/vite/routes/context.test.ts
new file mode 100644
index 000000000..71a0aee69
--- /dev/null
+++ b/packages/core/src/vite/routes/context.test.ts
@@ -0,0 +1,28 @@
+import { describe, expect, it } from 'vitest';
+import { decodePathSegment } from './context.ts';
+
+describe('decodePathSegment', () => {
+  it('decodes a percent-encoded non-ASCII segment', () => {
+    expect(decodePathSegment('%E5%B0%81%E9%9D%A2')).toBe('封面');
+  });
+
+  it('returns a plain segment unchanged', () => {
+    expect(decodePathSegment('cover')).toBe('cover');
+  });
+
+  it('decodes a percent-encoded filename with spaces and separators', () => {
+    expect(decodePathSegment('my%20photo%20(1).png')).toBe('my photo (1).png');
+  });
+
+  it('returns null for a truncated escape rather than throwing', () => {
+    expect(decodePathSegment('%E0%A4%A')).toBeNull();
+  });
+
+  it('returns null for a lone percent sign', () => {
+    expect(decodePathSegment('%')).toBeNull();
+  });
+
+  it('preserves the empty segment', () => {
+    expect(decodePathSegment('')).toBe('');
+  });
+});
diff --git a/packages/core/src/vite/routes/context.ts b/packages/core/src/vite/routes/context.ts
index d355b4b5a..a284c9c99 100644
--- a/packages/core/src/vite/routes/context.ts
+++ b/packages/core/src/vite/routes/context.ts
@@ -74,3 +74,26 @@ export function resolveSlidePath(
 export function resolveSlideEntryPath(ctx: ApiContext, slideId: string): string | null {
   return resolveSlidePath(ctx.userCwd, ctx.slidesDir, slideId);
 }
+
+/**
+ * Decode one URL path segment, reporting malformed percent-encoding as null
+ * instead of throwing.
+ *
+ * `decodeURIComponent` raises `URIError` on a truncated or invalid escape such
+ * as `%E0%A4%A` or a lone `%`. Inside a dev-server request handler that becomes
+ * an unhandled exception and a 500, which reads as a broken server rather than
+ * what it is: a request the client got wrong. Returning null lets each route
+ * answer 400 on its own terms, alongside the invalid-path rejections it already
+ * performs.
+ *
+ * Supporting non-ASCII slide ids is what makes this reachable in ordinary use.
+ * Every segment of an asset URL is percent-encoded on the way out now, so any
+ * segment can come back damaged.
+ */
+export function decodePathSegment(raw: string): string | null {
+  try {
+    return decodeURIComponent(raw);
+  } catch {
+    return null;
+  }
+}
diff --git a/packages/core/src/vite/routes/slides.ts b/packages/core/src/vite/routes/slides.ts
index 0e9ef2c33..ca8033492 100644
--- a/packages/core/src/vite/routes/slides.ts
+++ b/packages/core/src/vite/routes/slides.ts
@@ -16,7 +16,7 @@ import {
 } from '../../editing/slide-ops.ts';
 import { readManifest, writeManifest } from '../../files/folders.ts';
 import { validateMutationRequest } from '../../http/request-guard.ts';
-import { type ApiContext, json, readBody } from './context.ts';
+import { type ApiContext, decodePathSegment, json, readBody } from './context.ts';
 
 // PUT    /__slides/:id/reorder            reorder pages { order: number[] }
 // DELETE /__slides/:id/pages/:i           remove page
@@ -40,8 +40,9 @@ export function registerSlideRoutes(server: ViteDevServer, ctx: ApiContext): voi
         if (!requestCheck.ok) {
           return json(res, requestCheck.status, { error: requestCheck.error });
         }
-        const slideId = reorderMatch[1];
-        if (!SLIDE_ID_RE.test(slideId)) return json(res, 400, { error: 'invalid slideId' });
+        const slideId = decodePathSegment(reorderMatch[1]);
+        if (!slideId || !SLIDE_ID_RE.test(slideId))
+          return json(res, 400, { error: 'invalid slideId' });
 
         const body = (await readBody(req)) as { order?: unknown };
         if (!Array.isArray(body.order)) return json(res, 400, { error: 'invalid order' });
@@ -81,10 +82,11 @@ export function registerSlideRoutes(server: ViteDevServer, ctx: ApiContext): voi
 
       const pageOpMatch = url.pathname.match(/^\/([^/]+)\/pages\/(\d+)(?:\/([a-z]+))?$/);
       if (pageOpMatch) {
-        const slideId = pageOpMatch[1];
+        const slideId = decodePathSegment(pageOpMatch[1]);
         const pageIndex = Number.parseInt(pageOpMatch[2], 10);
         const op = pageOpMatch[3];
-        if (!SLIDE_ID_RE.test(slideId)) return json(res, 400, { error: 'invalid slideId' });
+        if (!slideId || !SLIDE_ID_RE.test(slideId))
+          return json(res, 400, { error: 'invalid slideId' });
         if (!Number.isInteger(pageIndex) || pageIndex < 0)
           return json(res, 400, { error: 'invalid page index' });
 
@@ -138,8 +140,9 @@ export function registerSlideRoutes(server: ViteDevServer, ctx: ApiContext): voi
         if (!requestCheck.ok) {
           return json(res, requestCheck.status, { error: requestCheck.error });
         }
-        const slideId = duplicateMatch[1];
-        if (!SLIDE_ID_RE.test(slideId)) return json(res, 400, { error: 'invalid slideId' });
+        const slideId = decodePathSegment(duplicateMatch[1]);
+        if (!slideId || !SLIDE_ID_RE.test(slideId))
+          return json(res, 400, { error: 'invalid slideId' });
 
         const body = (await readBody(req)) as DuplicateSlideBody;
         if (body.newId !== undefined && typeof body.newId !== 'string') {
@@ -160,8 +163,9 @@ export function registerSlideRoutes(server: ViteDevServer, ctx: ApiContext): voi
 
       const idMatch = url.pathname.match(/^\/([^/]+)$/);
       if (!idMatch) return next();
-      const slideId = idMatch[1];
-      if (!SLIDE_ID_RE.test(slideId)) return json(res, 400, { error: 'invalid slideId' });
+      const slideId = decodePathSegment(idMatch[1]);
+      if (!slideId || !SLIDE_ID_RE.test(slideId))
+        return json(res, 400, { error: 'invalid slideId' });
 
       if (method === 'PATCH') {
         const requestCheck = validateMutationRequest(req, { requireJsonBody: true });