diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 3e51630..6baa4ba 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -94,6 +94,12 @@ You can add a new language to Scrum Helper for your own use or contribute it to
 1. **Create a Locale Folder**
    - Go to `src/_locales`.
    - Create a new folder named with the [ISO language code](https://developer.chrome.com/docs/extensions/reference/i18n/#localeTable) (e.g., `it` for Italian, `fr` for French).
+   - **Important:** Use canonical locale codes to avoid duplicates:
+     - For Chinese (Simplified): use `zh_CN` (not `zh_Hans` or `zh-CN`)
+     - For Chinese (Traditional): use `zh_TW` (not `zh_Hant` or `zh-TW`)
+     - For Portuguese (Brazil): use `pt_BR` (not `pt-BR`)
+     - For English: use `en` (not `en_US` or `en-US`)
+   - Run `npm run validate:locales` to check for duplicate locale codes before submitting.
 
 2. **Add a `messages.json` File**
    - Copy the `messages.json` from `src/_locales/en/messages.json` or any other language as a template.
diff --git a/package.json b/package.json
index 7f533e8..b31e2b3 100644
--- a/package.json
+++ b/package.json
@@ -8,8 +8,9 @@
 	},
 	"scripts": {
 		"format": "biome format --write",
-		"check": "biome check .",
-		"fix": "biome lint --write"
+		"check": "biome check . && node scripts/validate-locales.js",
+		"fix": "biome lint --write",
+		"validate:locales": "node scripts/validate-locales.js"
 	},
 	"keywords": [
 		"scrum",
diff --git a/scripts/validate-locales.js b/scripts/validate-locales.js
new file mode 100644
index 0000000..82b1ac9
--- /dev/null
+++ b/scripts/validate-locales.js
@@ -0,0 +1,110 @@
+#!/usr/bin/env node
+
+/**
+ * Locale Duplication Validator
+ * 
+ * This script prevents duplicate locale folders that map to the same language.
+ * It helps avoid conflicts in translation management systems like Weblate.
+ * 
+ * For example, both 'zh_CN' and 'zh_Hans' map to "Chinese (Simplified)",
+ * which causes duplication issues.
+ */
+
+const fs = require('fs');
+const path = require('path');
+
+// Map of locale codes that should be considered duplicates
+// Key: canonical locale to keep, Value: array of duplicate codes to avoid
+const LOCALE_DUPLICATES = {
+	zh_CN: ['zh_Hans', 'zh-CN', 'zh-Hans'],
+	zh_TW: ['zh_Hant', 'zh-TW', 'zh-Hant'],
+	pt_BR: ['pt-BR'],
+	en: ['en_US', 'en-US'],
+};
+
+// Flatten the duplicate map to check against
+const getAllDuplicates = () => {
+	const duplicates = {};
+	for (const [canonical, alternates] of Object.entries(LOCALE_DUPLICATES)) {
+		for (const alt of alternates) {
+			duplicates[alt] = canonical;
+		}
+	}
+	return duplicates;
+};
+
+const validateLocales = () => {
+	const localesDir = path.join(__dirname, '..', 'src', '_locales');
+	
+	if (!fs.existsSync(localesDir)) {
+		console.error('❌ Error: _locales directory not found');
+		process.exit(1);
+	}
+
+	const folders = fs.readdirSync(localesDir, { withFileTypes: true })
+		.filter(dirent => dirent.isDirectory())
+		.map(dirent => dirent.name);
+
+	const duplicateMap = getAllDuplicates();
+	const errors = [];
+	const warnings = [];
+
+	// Check for known duplicates
+	for (const folder of folders) {
+		if (duplicateMap[folder]) {
+			errors.push(
+				`❌ Duplicate locale detected: '${folder}' should use '${duplicateMap[folder]}' instead`
+			);
+		}
+	}
+
+	// Check if multiple canonical versions exist for the same language
+	const canonicalPresent = {};
+	for (const [canonical, alternates] of Object.entries(LOCALE_DUPLICATES)) {
+		if (folders.includes(canonical)) {
+			canonicalPresent[canonical] = true;
+		}
+		for (const alt of alternates) {
+			if (folders.includes(alt)) {
+				if (canonicalPresent[canonical]) {
+					errors.push(
+						`❌ Conflict: Both '${canonical}' and '${alt}' exist. Keep only '${canonical}'`
+					);
+				}
+			}
+		}
+	}
+
+	// Validate each locale folder has messages.json
+	for (const folder of folders) {
+		const messagesPath = path.join(localesDir, folder, 'messages.json');
+		if (!fs.existsSync(messagesPath)) {
+			warnings.push(`⚠️  Warning: '${folder}' is missing messages.json`);
+		}
+	}
+
+	// Report results
+	console.log('\n🔍 Locale Validation Report\n');
+	console.log(`Found ${folders.length} locale folder(s): ${folders.join(', ')}`);
+	console.log('');
+
+	if (errors.length > 0) {
+		console.error('Errors found:\n');
+		errors.forEach(err => console.error(err));
+		console.error('\n💡 Tip: Use the canonical locale codes defined in Chrome i18n standards.');
+		console.error('   See: https://developer.chrome.com/docs/extensions/reference/api/i18n\n');
+		process.exit(1);
+	}
+
+	if (warnings.length > 0) {
+		console.warn('Warnings:\n');
+		warnings.forEach(warn => console.warn(warn));
+		console.warn('');
+	}
+
+	console.log('✅ All locale folders are valid. No duplicates detected.\n');
+	process.exit(0);
+};
+
+// Run validation
+validateLocales();