Add localization for mhchem error messages.

components/mjs/input/tex/extensions/mhchem/config.json

@@ -5,6 +5,12 @@
     "targets": ["input/tex/mhchem"],
     "excludeSubdirs": true
   },
+  "copy": {
+    "to": "[bundle]/input/tex/extensions/mhchem",
+    "from": "[ts]/input/tex/mhchem",
+    "copy": ["__locales__"],
+    "excludes": ["__locales__/Component.ts"]
+  },
   "webpack": {
     "name": "input/tex/extensions/mhchem",
     "libs": [

testsuite/tests/input/tex/Mhchem.test.ts

@@ -486,10 +486,14 @@ describe('Mhchem-Ams', () => {
     ).toMatchSnapshot();
   });
 
-  it('Mhchem Error', () => {
+  it('Mhchem Bond Error', () => {
     expectTexError('\\ce{A\\bond{x}B}').toBe('mhchem bug T. Please report.');
   });
 
+  it('Mhchem Brace Error', () => {
+    expectTexError('\\ce{{x^${x}}}').toBe('Extra close brace or missing open brace');
+  });
+
   it('Mhchem stretchy <-', () => {
     expect(tex2mml('\\ce{A <-[text] B}')).toMatchSnapshot();
   });

ts/input/tex/mhchem/MhchemConfiguration.ts

@@ -32,6 +32,8 @@ import BaseMethods from '../base/BaseMethods.js';
 import { AmsMethods } from '../ams/AmsMethods.js';
 import { mhchemParser } from '#mhchem/mhchemParser.js';
 import { TEXCLASS } from '../../../core/MmlTree/MmlNode.js';
+import { COMPONENT } from './__locales__/Component.js';
+export { COMPONENT };
 
 /**
  * Creates mo token elements with the proper attributes
@@ -104,8 +106,20 @@ export const MhchemMethods: { [key: string]: ParseMethod } = {
       for (const [name, pattern] of MhchemReplacements.entries()) {
         tex = tex.replace(pattern, name as string);
       }
-    } catch (err) {
-      throw new TexError(null, err[0], err[1]);
+    } catch ([id, msg]) {
+      if (id === 'MhchemErrorBond') {
+        const match = msg.match(/\((.*)\)/);
+        throw new TexError(COMPONENT, id, match[1]);
+      }
+      if (id.startsWith('MhchemBug')) {
+        const match = msg.match(/mhchem bug (.).*\((.*)\)/);
+        if (match) {
+          throw new TexError(COMPONENT, 'MhchemBug2', match[1], match[2]);
+        } else {
+          throw new TexError(COMPONENT, 'MhchemBug', id.charAt(9));
+        }
+      }
+      throw new TexError('[tex]/base', id);
     }
     parser.string = tex + parser.string.substring(parser.i);
     parser.i = 0;

ts/input/tex/mhchem/__locales__/Component.ts

@@ -0,0 +1,28 @@
+/*************************************************************
+ *
+ *  Copyright (c) 2026 The MathJax Consortium
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+/**
+ * @file  Locale component registration for [tex]/mhchem
+ *
+ * @author dpvc@mathjax.org (Davide P. Cervone)
+ */
+
+import { Locale } from '../../../../util/Locale.js';
+
+export const COMPONENT = '[tex]/mhchem';
+
+Locale.registerLocaleFiles(COMPONENT, '../ts/input/tex/bbox');

ts/input/tex/mhchem/__locales__/de.json

@@ -0,0 +1,5 @@
+{
+  "MhchemBug": "mhchem-Fehler %1. Bitte melden.",
+  "MhchemBug2": "mhchem-Fehler %1. Bitte melden. (%2)",
+  "MhchemErrorBond": "mhchem-Fehler. Unbekannter Bindungstyp (%1)"
+}

ts/input/tex/mhchem/__locales__/en.json

@@ -0,0 +1,5 @@
+{
+  "MhchemBug": "mhchem bug %1. Please report.",
+  "MhchemBug2": "mhchem bug %1. Please report. (%2)",
+  "MhchemErrorBond": "mhchem Error. Unknown bond type (%1)"
+}