diff --git a/ui/src/ui/markdown.test.ts b/ui/src/ui/markdown.test.ts
index f637d4726a5..27bd5db94d4 100644
--- a/ui/src/ui/markdown.test.ts
+++ b/ui/src/ui/markdown.test.ts
@@ -1,5 +1,6 @@
 import { render } from "lit";
 import { describe, expect, it, vi } from "vitest";
+import { i18n } from "../i18n/index.ts";
 import { md, toSanitizedMarkdownHtml } from "./markdown.ts";
 import { renderMarkdownSidebar } from "./views/markdown-sidebar.ts";
 
@@ -317,6 +318,23 @@ describe("toSanitizedMarkdownHtml", () => {
       expect(html).toContain("data-code=");
     });
 
+    it("keeps localized copy labels fresh after locale changes", async () => {
+      const markdown = "```ts\nconst localizedCopy = true;\n```";
+      await i18n.setLocale("en");
+      const english = toSanitizedMarkdownHtml(markdown);
+
+      try {
+        await i18n.setLocale("zh-CN");
+        const chinese = toSanitizedMarkdownHtml(markdown);
+
+        expect(english).toContain(">Copy<");
+        expect(chinese).toContain(">复制<");
+        expect(chinese).not.toContain(">Copy<");
+      } finally {
+        await i18n.setLocale("en");
+      }
+    });
+
     it("collapses JSON code blocks", () => {
       const html = toSanitizedMarkdownHtml('```json\n{"key": "value"}\n```');
       expect(html).toContain("<details");
diff --git a/ui/src/ui/markdown.ts b/ui/src/ui/markdown.ts
index faf20c9a9e9..5efac70871d 100644
--- a/ui/src/ui/markdown.ts
+++ b/ui/src/ui/markdown.ts
@@ -1,7 +1,7 @@
 import DOMPurify from "dompurify";
 import MarkdownIt from "markdown-it";
 import markdownItTaskLists from "markdown-it-task-lists";
-import { t } from "../i18n/index.ts";
+import { i18n, t } from "../i18n/index.ts";
 import { truncateText } from "./format.ts";
 import { normalizeLowercaseStringOrEmpty } from "./string-coerce.ts";
 
@@ -481,8 +481,9 @@ export function toSanitizedMarkdownHtml(markdown: string): string {
     return "";
   }
   installHooks();
+  const cacheKey = `${i18n.getLocale()}\0${input}`;
   if (input.length <= MARKDOWN_CACHE_MAX_CHARS) {
-    const cached = getCachedMarkdown(input);
+    const cached = getCachedMarkdown(cacheKey);
     if (cached !== null) {
       return cached;
     }
@@ -498,7 +499,7 @@ export function toSanitizedMarkdownHtml(markdown: string): string {
     const html = renderEscapedPlainTextHtml(`${truncated.text}${suffix}`);
     const sanitized = DOMPurify.sanitize(html, sanitizeOptions);
     if (input.length <= MARKDOWN_CACHE_MAX_CHARS) {
-      setCachedMarkdown(input, sanitized);
+      setCachedMarkdown(cacheKey, sanitized);
     }
     return sanitized;
   }
@@ -513,7 +514,7 @@ export function toSanitizedMarkdownHtml(markdown: string): string {
   }
   const sanitized = DOMPurify.sanitize(rendered, sanitizeOptions);
   if (input.length <= MARKDOWN_CACHE_MAX_CHARS) {
-    setCachedMarkdown(input, sanitized);
+    setCachedMarkdown(cacheKey, sanitized);
   }
   return sanitized;
 }