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Documentation Index

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Bolna Voice AI automatically detects the language your callers speak and switches system messages to match. No manual intervention needed. The agent analyzes the conversation and delivers the right message in the right language.

User Online Check

“Are you still there?” plays in the caller’s detected language

Call Hangup

Farewell message delivered in the detected language

Tool Call Wait

“Please wait” messages during API calls adapt to the language

How Detection Works

1

Conversation Begins

The agent starts in the primary language configured in the Audio Tab.
2

Language Analysis

After 3 conversation turns, Bolna analyzes the caller’s transcripts to identify the dominant language being spoken.
3

Auto-Switch

Once detected, all configured system messages switch to that language for the rest of the call.
Detection waits for 3 turns to gather enough context for accurate identification. This keeps it fast while avoiding false matches early in the call.

Supported Message Types

User Online Check Message

When the agent checks if a caller is still on the line after a period of silence, it sends a configurable message. Add variants in multiple languages and Bolna picks the right one automatically.
User online detection settings with multilingual message fields for English, Hindi, Gujarati, Bengali, and Tamil
{
  "check_user_online_message": {
    "en": "Hey, are you still there?",
    "hi": "क्या आप अभी भी वहाँ हैं?",
    "ta": "வணக்கம், நீங்கள் இன்னும் இணைப்பில் இருக்கிறீர்களா?",
    "bn": "নমস্কার, আপনি কি এখনও লাইনে আছেন?"
  }
}

Call Hangup Message

When the agent ends a call, it delivers a closing message. Configure multilingual variants so callers hear a natural farewell in their language.
Call settings showing multilingual hangup message fields for English, Hindi, Bengali, and Tamil
{
  "call_hangup_message": {
    "en": "Thank you for calling. Goodbye!",
    "hi": "कॉल करने के लिए धन्यवाद। अलविदा!",
    "bn": "কলটি এখন কেটে যাবে। ধন্যবাদ এবং নমস্কার!"
  }
}

Function Tool Call Messages

When the agent executes a tool or API call, it plays a brief “please wait” message. This message can also be configured per language.
Custom function configuration showing pre_call_message JSON with English and Hindi variants
{
  "pre_call_message": {
    "en": "Just give me a moment, I'll be back with you.",
    "hi": "कृपया थोड़ा समय दीजिए, मैं पता करके बताता हूँ।"
  }
}

Fallback Behavior

When selecting a message, Bolna follows a three-step fallback:
PriorityWhat happens
1. Detected languageUses the message in the caller’s detected language
2. EnglishFalls back to the en variant if the detected language is not configured
3. First availableUses the first language in the configuration if neither is found
Always configure an en (English) variant as a safe fallback for every message type.

Supported Languages

Auto-detection supports all languages available in Bolna, identified by their ISO 639-1 codes.
CodeLanguageCodeLanguageCodeLanguage
enEnglishhiHindibnBengali
taTamilteTelugumrMarathi
guGujaratiknKannadamlMalayalam
paPunjabiurUrduasAssamese
For the full list of supported languages, see the Multilingual Support guide.

Best Practices

Consistent Coverage

Add message variants for every language your agent supports. Gaps lead to unexpected fallbacks.

Culturally Appropriate

Write messages that feel natural in each language. Avoid direct translations.

Native Script

Always use the language’s native script. “धन्यवाद” not “Dhanyavaad”.

Test with Speakers

Verify messages sound natural by testing with native speakers of each language.

Next Steps

Multilingual Support

Full guide to setting up multilingual agents

Non-English Prompts

Best practices for writing prompts in native scripts

Custom Function Calls

Configure pre-call messages for API tools

Engine Tab

Configure user online detection and timeouts