diff --git a/webui/package.json b/webui/package.json
index 31b41a3..de1f37d 100644
--- a/webui/package.json
+++ b/webui/package.json
@@ -22,9 +22,11 @@
   },
   "scripts": {
     "dev": "vite --host 127.0.0.1 --port 5173",
+    "prebuild": "npm run audit:i18n-structural",
     "build": "tsc && vite build",
     "preview": "vite preview --host 127.0.0.1 --port 4173",
     "audit:i18n-structural": "node scripts/audit-i18n-structural.mjs",
+    "test:i18n-catalog": "node --test tests/i18n-catalog-validation.test.mjs",
     "test:file-drop-zone": "rm -rf .file-drop-test-build && mkdir -p .file-drop-test-build && printf '{\"type\":\"commonjs\"}\\n' > .file-drop-test-build/package.json && tsc -p tsconfig.file-drop-tests.json && node .file-drop-test-build/tests/file-drop-resolver.test.js && node scripts/test-file-drop-zone-structure.mjs",
     "test:data-grid-actions": "rm -rf .component-test-build && mkdir -p .component-test-build && printf '{\"type\":\"commonjs\"}\\n' > .component-test-build/package.json && tsc -p tsconfig.component-tests.json && node .component-test-build/tests/data-grid-actions.test.js",
     "test:dialog-focus": "rm -rf .component-test-build && mkdir -p .component-test-build && printf '{\"type\":\"commonjs\"}\\n' > .component-test-build/package.json && tsc -p tsconfig.component-tests.json && node .component-test-build/tests/dialog-focus.test.js && node scripts/test-dialog-focus-structure.mjs",
diff --git a/webui/scripts/audit-i18n-structural.mjs b/webui/scripts/audit-i18n-structural.mjs
index d4e7f14..c0e7cd7 100644
--- a/webui/scripts/audit-i18n-structural.mjs
+++ b/webui/scripts/audit-i18n-structural.mjs
@@ -4,6 +4,7 @@ import path from "node:path";
 import { fileURLToPath } from "node:url";
 import vm from "node:vm";
 import ts from "typescript";
+import { findDuplicateTranslationKeys } from "./i18n-catalog-validation.mjs";
 
 const scriptDir = path.dirname(fileURLToPath(import.meta.url));
 const webuiDir = path.resolve(scriptDir, "..");
@@ -74,6 +75,8 @@ function scanStructuralSourcePositions(roots) {
 function scanGeneratedCatalogs(files) {
   const findings = [];
   for (const file of files) {
+    const source = fs.readFileSync(file, "utf8");
+    findings.push(...findDuplicateTranslationKeys(source, file));
     const translations = loadGeneratedTranslations(file);
     for (const [language, dictionary] of Object.entries(translations)) {
       for (const [key, value] of Object.entries(dictionary)) {
diff --git a/webui/scripts/i18n-catalog-validation.mjs b/webui/scripts/i18n-catalog-validation.mjs
new file mode 100644
index 0000000..d531387
--- /dev/null
+++ b/webui/scripts/i18n-catalog-validation.mjs
@@ -0,0 +1,69 @@
+import ts from "typescript";
+
+export function findDuplicateTranslationKeys(sourceText, fileName = "generatedTranslations.ts") {
+  const source = ts.createSourceFile(
+    fileName,
+    sourceText,
+    ts.ScriptTarget.Latest,
+    true,
+    ts.ScriptKind.TS
+  );
+  const findings = [];
+
+  function visit(node) {
+    if (
+      ts.isVariableDeclaration(node) &&
+      ts.isIdentifier(node.name) &&
+      node.name.text === "generatedTranslations" &&
+      node.initializer &&
+      ts.isObjectLiteralExpression(node.initializer)
+    ) {
+      scanCatalog(node.initializer);
+    }
+    ts.forEachChild(node, visit);
+  }
+
+  function scanCatalog(catalog) {
+    for (const localeProperty of catalog.properties) {
+      if (!ts.isPropertyAssignment(localeProperty) || !ts.isObjectLiteralExpression(localeProperty.initializer)) {
+        continue;
+      }
+      const locale = propertyName(localeProperty.name);
+      const firstDeclarations = new Map();
+      for (const translationProperty of localeProperty.initializer.properties) {
+        if (!ts.isPropertyAssignment(translationProperty)) continue;
+        const key = propertyName(translationProperty.name);
+        if (!key) continue;
+        const first = firstDeclarations.get(key);
+        if (!first) {
+          firstDeclarations.set(key, translationProperty.name);
+          continue;
+        }
+        const duplicatePosition = source.getLineAndCharacterOfPosition(
+          translationProperty.name.getStart(source)
+        );
+        const firstPosition = source.getLineAndCharacterOfPosition(first.getStart(source));
+        findings.push(
+          `${fileName}:${duplicatePosition.line + 1}:${duplicatePosition.character + 1} ` +
+          `duplicate generated translation key ${JSON.stringify(key)} in locale ` +
+          `${JSON.stringify(locale)}; first declared at line ${firstPosition.line + 1}`
+        );
+      }
+    }
+  }
+
+  visit(source);
+  return findings;
+}
+
+function propertyName(name) {
+  if (
+    ts.isIdentifier(name) ||
+    ts.isStringLiteral(name) ||
+    ts.isNumericLiteral(name) ||
+    ts.isNoSubstitutionTemplateLiteral(name)
+  ) {
+    return name.text;
+  }
+  return "";
+}
diff --git a/webui/tests/i18n-catalog-validation.test.mjs b/webui/tests/i18n-catalog-validation.test.mjs
new file mode 100644
index 0000000..59f66de
--- /dev/null
+++ b/webui/tests/i18n-catalog-validation.test.mjs
@@ -0,0 +1,38 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+
+import { findDuplicateTranslationKeys } from "../scripts/i18n-catalog-validation.mjs";
+
+test("allows the same translation key once in each locale", () => {
+  const source = `
+    export const generatedTranslations = {
+      en: { "i18n:example.share.12345678": "Share" },
+      de: { "i18n:example.share.12345678": "Freigeben" }
+    };
+  `;
+
+  assert.deepEqual(findDuplicateTranslationKeys(source), []);
+});
+
+test("rejects duplicate keys within a generated locale catalog", () => {
+  const source = `
+    export const generatedTranslations = {
+      en: {
+        "i18n:example.share.12345678": "Share",
+        "i18n:example.share.12345678": "Share"
+      },
+      de: {
+        "i18n:example.share.12345678": "Freigabe",
+        "i18n:example.share.12345678": "Freigeben"
+      }
+    };
+  `;
+
+  const findings = findDuplicateTranslationKeys(source, "fixture.ts");
+
+  assert.equal(findings.length, 2);
+  assert.match(findings[0], /fixture\.ts:\d+:\d+ duplicate generated translation key/);
+  assert.match(findings[0], /locale "en"/);
+  assert.match(findings[1], /locale "de"/);
+  assert.ok(findings.every((finding) => finding.includes("first declared at line")));
+});