diff --git a/src/settings.ts b/src/settings.ts
index ae2159f..cc0d394 100644
--- a/src/settings.ts
+++ b/src/settings.ts
@@ -37,7 +37,7 @@ export const DEFAULT_SETTINGS: PluginSettings = {
   apiMaxTokens: 4096,
   maxDocChars: MAX_DOC_CHARS,
   maxCacheEntries: DEFAULT_MAX_CACHE_ENTRIES,
-  promptLanguage: 'zh',
+  promptLanguage: 'auto',
   minCards: 5,
   maxCards: 15,
   customSystemPrompt: '',
diff --git a/tests/direct-prompt.test.js b/tests/direct-prompt.test.js
index ea78c3d..633e490 100644
--- a/tests/direct-prompt.test.js
+++ b/tests/direct-prompt.test.js
@@ -83,7 +83,7 @@ const { assert, requireBundledModule, cleanup } = require('./direct-test-setup')
 
     // ── buildPrompts: invalid promptLanguage falls back ──
     const badLang = prompt.buildPrompts('doc', { ...base, promptLanguage: 'xyz' });
-    assert.ok(badLang.system.includes('中文'), 'invalid promptLanguage falls back to zh default');
+    assert.ok(badLang.system.includes('main language'), 'invalid promptLanguage falls back to auto default');
 
     // ── buildPrompts: card count normalization ──
     // 0 is falsy so || picks DEFAULT (5), then Math.max(1, 5) = 5