Why does the AI SDR reply in the wrong language, and how do I enforce a specific reply language?
How AI SDR language detection works, why it can pick the wrong language, and how to enforce a reply language via the KB.
The AI SDR mirrors the language of the prospect's most recent message. Most of the time that works. When it doesn't, it's almost always because something other than the prospect's actual words influenced the detection — a Spanish email signature on an English reply, locale headers set to German by an IT department, or quoted text from a previous message in a different language.
There is no per-workspace language setting today. Language control is done entirely through knowledge base instructions.
How language detection works
The AI SDR reads the prospect's latest message and replies in whatever language that message appears to be written in. It does not check the workspace locale or any campaign-level setting — it mirrors what it sees.
That means:
- English message in, English reply out.
- French message in, French reply out.
- Mixed-language message — the AI picks the dominant language, which may not always be what you expect.
Why it sometimes gets it wrong
The AI reads the full message, including parts that aren't the prospect's own words. Common triggers for misdetection:
| Trigger | Example |
|---|---|
| Signature block | Prospect writes in English but their signature includes a Spanish tagline or legal disclaimer. The AI sees Spanish text and replies in Spanish. |
| Quoted reply text | The prospect forwards an internal thread in German, then adds one line of English at the top. The German quoted text outweighs the English line. |
| Email client locale headers | The prospect's Outlook is set to French. Some clients embed locale metadata that the AI can pick up on, even when the message body is in English. |
| Auto-translated snippets | A prospect pastes a machine-translated section into an otherwise English email. |
In all of these cases, the prospect intended to communicate in one language, but the surrounding metadata or boilerplate pointed the AI toward another.
How to enforce a reply language via the knowledge base
Add a clear, standalone instruction to the top of your Knowledge Base on Settings -> AI SDR Agent. Here are examples depending on what you need:
Always reply in one language, regardless of what the prospect writes:
Language rule: Always reply in English regardless of the language
the prospect writes in. Never switch to another language.Match the prospect's message body only (ignore signatures and quoted text):
Language rule: Reply in the language the prospect's message body
is written in. Ignore signature blocks, quoted replies, and email
headers when determining the language.Support a specific set of languages:
Language rule: Reply in English or French only. If the prospect
writes in another language, reply in English.Tips for writing effective language instructions
- Put the instruction at the top of the KB. Don't bury it inside a product FAQ entry — the AI is more likely to follow rules that appear early and stand alone.
- Be explicit about what to ignore. "Ignore signature blocks and quoted replies" helps the AI focus on the prospect's actual words.
- Be specific about fallback. If you say "reply in the prospect's language," also say what to do when the language is ambiguous — otherwise the AI guesses.
- One rule, not three. Don't add contradictory language rules in different parts of the KB. Keep it to a single, clear statement.
After updating the KB
- Click Save Settings at the bottom of the page.
- The new rule takes effect on the next reply the AI generates. In-flight conversations keep the language they started with — you'll see the change on new threads and on the next follow-up for threads that haven't replied yet.
KB language rules work most of the time, not every time
Language instructions are guidance, not a hard switch. The AI follows them in the vast majority of cases, but an especially long signature block or a heavily quoted thread can still tip detection the wrong way. If a specific thread keeps replying in the wrong language, take it over manually and reply yourself.