Skip to main content
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

The Agent Switches Language

Bolna’s language-switching engine decides, turn by turn, whether the caller has genuinely moved to a different configured language. See How Language Switching Works for exactly what triggers this.
3

System Messages Follow

These system messages simply follow whatever language the agent is currently speaking — when it switches mid-call, they switch with it too, near-instantly, falling back to English if a variant is missing.
There’s no separate detection pass for system messages — they always match the agent’s current active language.

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

Multilingual user online check messages configured for English, Hindi, Gujarati, Bengali, and Tamil


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

Multilingual call hangup messages configured for English, Hindi, Bengali, and Tamil


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

Multilingual pre-call messages for custom function tools in English and Hindi


Fallback Behavior

When selecting a message, Bolna follows a three-step fallback:
Always configure an en (English) variant as a safe fallback for every message type.

Supported Languages

System messages follow the same language the agent itself is speaking, so they cover whatever your agent supports. Automatic mid-call detection — the part that decides when the agent’s active language changes — is tuned for a specific set of languages; see Supported Languages for Automatic Detection for that exact list, and the Multilingual Support guide for the full set of languages Bolna can be configured with.

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

How Language Switching Works

What triggers a switch, and what doesn’t

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