From bdda0ca08207c0610d7cf2afe3dec1472b839852 Mon Sep 17 00:00:00 2001
From: Stephen Smith <stephen@vapi.ai>
Date: Mon, 19 Oct 2026 12:41:02 -0700
Subject: [PATCH] Added best practices for language selection

---
 fern/observability/simulations-configure-ai-tester.mdx | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/fern/observability/simulations-configure-ai-tester.mdx b/fern/observability/simulations-configure-ai-tester.mdx
index 04c4500c1..d5fc65151 100644
--- a/fern/observability/simulations-configure-ai-tester.mdx
+++ b/fern/observability/simulations-configure-ai-tester.mdx
@@ -59,10 +59,14 @@ Chat simulations ignore transcriber and voice settings. Behavior, model, and tur
   </Step>
 
   <Step title="Configure voice settings">
-    For a voice simulation, configure these optional settings:
+    For a voice simulation, configure these optional settings by expanding **Advanced settings**:
 
     - Under **Transcriber**, select the speech-to-text provider, language, and model.
     - Under **Voice**, select the provider and voice, or enter a custom voice ID.
+
+    <Note>
+      Set the AI tester's transcriber to match the language used by the assistant or squad you're testing, or use a transcriber that supports [automatic language detection](/customization/multilingual#configure-automatic-language-detection). Otherwise, the AI tester may not understand the replies and may repeat the same questions. Also select a model and voice that support the same language.
+    </Note>
   </Step>
 
   <Step title="Continue configuring the suite">
@@ -161,6 +165,10 @@ curl -X PATCH "https://api.vapi.ai/eval/simulation/personality/<personality-id>"
   }'
 ```
 
+<Note>
+  For a voice simulation, set the AI tester's `transcriber` to match the language used by the assistant or squad you're testing, or use a transcriber that supports [automatic language detection](/customization/multilingual#configure-automatic-language-detection). Otherwise, the AI tester may not understand the replies and may repeat the same questions. Also set a `model` and `voice` that support the same language. The transcriber's language field varies by provider, such as `language` for Deepgram or `language` and `languages` for Soniox.
+</Note>
+
 Within a personality's `assistant` configuration, `assistant-speaks-first` means the AI tester starts the conversation. Use `assistant-waits-for-user` when the assistant or squad under test should start.
 
 In `stopSpeakingPlan`, `voiceSeconds` only applies when `numWords` is `0`. When `numWords` is greater than `0`, the AI tester waits for that number of transcribed words instead. See [**Stop speaking plan**](/customization/voice-pipeline-configuration#stop-speaking-plan) for details.