diff --git a/packages/hydrooj/package.json b/packages/hydrooj/package.json
index e5ae9917c..e0256fa2a 100644
--- a/packages/hydrooj/package.json
+++ b/packages/hydrooj/package.json
@@ -1,6 +1,6 @@
 {
     "name": "hydrooj",
-    "version": "2.26.12",
+    "version": "2.26.13",
     "bin": "bin/hydrooj.js",
     "main": "dist/loader.js",
     "typings": "dist/loader.d.ts",
diff --git a/packages/hydrooj/src/handler/contest.ts b/packages/hydrooj/src/handler/contest.ts
index dea587291..d4a7103de 100644
--- a/packages/hydrooj/src/handler/contest.ts
+++ b/packages/hydrooj/src/handler/contest.ts
@@ -4,7 +4,7 @@ import AdmZip from 'adm-zip';
 import { isSafeInteger } from 'lodash';
 import {
     ContestNotLiveError, ValidationError, ProblemNotFoundError,
-    ContestNotAttendedError, PermissionError,
+    ContestNotAttendedError, PermissionError, BadRequestError,
 } from '../error';
 import { ProblemDoc, Tdoc, User } from '../interface';
 import paginate from '../lib/paginate';
@@ -344,6 +344,9 @@ class ContestDetailProblemSubmitHandler extends ContestProblemHandler {
     @param('lang', Types.Name)
     @param('code', Types.Content)
     async post(domainId: string, tid: ObjectID, lang: string, code: string) {
+        if (this.response.body.pdoc.config.langs && !this.response.body.pdoc.config.langs.includes('lang')) {
+            throw new BadRequestError('Language not allowed.');
+        }
         await this.limitRate('add_record', 60, 10);
         const rid = await record.add(domainId, this.pdoc.docId, this.user._id, lang, code, true, {
             type: document.TYPE_CONTEST,
diff --git a/packages/hydrooj/src/handler/problem.ts b/packages/hydrooj/src/handler/problem.ts
index 2b7b35b53..7c60e8a75 100644
--- a/packages/hydrooj/src/handler/problem.ts
+++ b/packages/hydrooj/src/handler/problem.ts
@@ -264,6 +264,9 @@ export class ProblemSubmitHandler extends ProblemDetailHandler {
     @param('lang', Types.Name)
     @param('code', Types.Content)
     async post(domainId: string, lang: string, code: string) {
+        if (this.response.body.pdoc.config.langs && !this.response.body.pdoc.config.langs.includes('lang')) {
+            throw new BadRequestError('Language not allowed.');
+        }
         await this.limitRate('add_record', 60, 5);
         const rid = await record.add(domainId, this.pdoc.docId, this.user._id, lang, code, true);
         const [rdoc] = await Promise.all([
diff --git a/packages/hydrooj/src/interface.ts b/packages/hydrooj/src/interface.ts
index fe7942761..fc963df5f 100644
--- a/packages/hydrooj/src/interface.ts
+++ b/packages/hydrooj/src/interface.ts
@@ -143,19 +143,20 @@ export interface SubtaskConfig {
 }
 
 export interface ProblemConfig {
-    type?: ProblemType,
-    score?: number,
-    time?: string,
-    memory?: string,
-    filename?: string,
-    checker_type?: string,
-    checker?: string,
-    interactor?: string,
-    user_extra_files?: string[],
-    judge_extra_files?: string[],
-    outputs?: [string, number][],
-    cases?: TestCaseConfig[],
-    subtasks?: SubtaskConfig[],
+    type?: ProblemType;
+    score?: number;
+    time?: string;
+    memory?: string;
+    filename?: string;
+    checker_type?: string;
+    checker?: string;
+    interactor?: string;
+    user_extra_files?: string[];
+    judge_extra_files?: string[];
+    outputs?: [string, number][];
+    cases?: TestCaseConfig[];
+    subtasks?: SubtaskConfig[];
+    langs?: string[];
 }
 
 export interface PlainContentNode {
diff --git a/packages/hydrooj/src/lib/testdataConfig.ts b/packages/hydrooj/src/lib/testdataConfig.ts
index efc9345c9..c6f02b7a3 100644
--- a/packages/hydrooj/src/lib/testdataConfig.ts
+++ b/packages/hydrooj/src/lib/testdataConfig.ts
@@ -3,11 +3,12 @@ import { load } from 'js-yaml';
 import type { ProblemConfig } from '../interface';
 
 interface ParseResult {
-    count: number,
-    memoryMax: number,
-    memoryMin: number,
-    timeMax: number,
-    timeMin: number,
+    count: number;
+    memoryMax: number;
+    memoryMin: number;
+    timeMax: number;
+    timeMin: number;
+    langs?: string[];
 }
 
 export async function parseConfig(config: string | ProblemConfig = {}) {
@@ -40,6 +41,7 @@ export async function parseConfig(config: string | ProblemConfig = {}) {
     if (result.timeMax < result.timeMin) {
         result.timeMax = result.timeMin = 1000;
     }
+    if (cfg.langs) result.langs = cfg.langs;
     return result;
 }
 
diff --git a/packages/hydrooj/src/model/discussion.ts b/packages/hydrooj/src/model/discussion.ts
index feda948dd..563a35485 100644
--- a/packages/hydrooj/src/model/discussion.ts
+++ b/packages/hydrooj/src/model/discussion.ts
@@ -284,7 +284,8 @@ const t = Math.exp(-0.15);
 
 async function updateSort() {
     const cursor = document.coll.find({ docType: document.TYPE_DISCUSSION });
-    while (cursor.hasNext()) {
+    // eslint-disable-next-line no-await-in-loop
+    while (await cursor.hasNext()) {
         // eslint-disable-next-line no-await-in-loop
         const data = await cursor.next();
         // eslint-disable-next-line no-await-in-loop
diff --git a/packages/ui-default/components/scratchpad/ScratchpadToolbarContainer.jsx b/packages/ui-default/components/scratchpad/ScratchpadToolbarContainer.jsx
index b7fef7b7f..4c8ee15e1 100644
--- a/packages/ui-default/components/scratchpad/ScratchpadToolbarContainer.jsx
+++ b/packages/ui-default/components/scratchpad/ScratchpadToolbarContainer.jsx
@@ -78,6 +78,11 @@ export default connect(mapStateToProps, mapDispatchToProps)(class ScratchpadTool
   }
 
   render() {
+    const LANGS = {};
+    for (const key in window.LANGS) {
+      if (UiContext.pdoc.config.langs && !UiContext.pdoc.config.langs.includes(key)) continue;
+      LANGS[key] = window.LANGS[key];
+    }
     return (
       <Toolbar>
         <ToolbarButton
@@ -136,7 +141,7 @@ export default connect(mapStateToProps, mapDispatchToProps)(class ScratchpadTool
             value={this.props.editorLang}
             onChange={(ev) => this.props.setEditorLanguage(ev.target.value)}
           >
-            {_.map(window.LANGS, (val, key) => (
+            {_.map(LANGS, (val, key) => (
               <option value={key} key={key}>{val.display}</option>
             ))}
           </select>
diff --git a/packages/ui-default/package.json b/packages/ui-default/package.json
index aadda825e..56f04f5d3 100644
--- a/packages/ui-default/package.json
+++ b/packages/ui-default/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@hydrooj/ui-default",
-  "version": "4.8.25",
+  "version": "4.8.26",
   "author": "undefined <i@undefined.moe>",
   "license": "AGPL-3.0",
   "main": "hydro.js",
diff --git a/packages/ui-default/pages/problem_submit.page.js b/packages/ui-default/pages/problem_submit.page.js
index 8c907d8f3..fdcb516da 100644
--- a/packages/ui-default/pages/problem_submit.page.js
+++ b/packages/ui-default/pages/problem_submit.page.js
@@ -15,12 +15,13 @@ const page = new NamedPage(['problem_submit', 'contest_detail_problem_submit'],
   $('#codelang-main-select').on('change', function () {
     const options = {};
     for (const key in window.LANGS) {
+      if (UiContext.pdocConfig.langs && !UiContext.pdocConfig.langs.includes(key)) continue;
       if (key.startsWith(`${this.value}.`) && key !== this.value) options[key] = window.LANGS[key].display;
     }
     if (Object.keys(options).length > 1) {
       setOptions($('#codelang-sub-select'), options);
       $('#codelang-sub-container').show();
-      $('[name="codeLang"]').val($('#codelang-sub-container').val());
+      $('[name="codeLang"]').val($('#codelang-sub-select').val());
     } else {
       $('#codelang-sub-container').hide();
       $('[name="codeLang"]').val(this.value);
@@ -31,6 +32,7 @@ const page = new NamedPage(['problem_submit', 'contest_detail_problem_submit'],
   });
   const main = {};
   for (const key in window.LANGS) {
+    if (UiContext.pdocConfig.langs && !UiContext.pdocConfig.langs.includes(key)) continue;
     if (!key.includes('.')) main[key] = window.LANGS[key].display;
   }
   setOptions($('#codelang-main-select'), main);
@@ -38,7 +40,8 @@ const page = new NamedPage(['problem_submit', 'contest_detail_problem_submit'],
   if (current.includes('.')) {
     const [m, s] = current.split('.');
     $('#codelang-main-select').val(m);
-    $('#codelang-sub-select').val(s).show();
+    $('#codelang-sub-select').val(s);
+    $('#codelang-sub-container').show();
   } else $('#codelang-main-select').val(current);
 });
 
diff --git a/packages/ui-default/templates/problem_submit.html b/packages/ui-default/templates/problem_submit.html
index bb58c2fcf..4a3a04171 100644
--- a/packages/ui-default/templates/problem_submit.html
+++ b/packages/ui-default/templates/problem_submit.html
@@ -1,5 +1,6 @@
 {% extends "layout/basic.html" %}
 {% block content %}
+{{ set(UiContext, 'pdocConfig', pdoc.config) }}
 <div class="row">
   <div class="medium-9 columns">
   {% if not tdoc or rdocs.length %}