You want Copilot in Outlook to compose email replies in a language other than your default Microsoft 365 profile language. By default, Copilot uses the language set in your Microsoft 365 account settings or the language of the email you are replying to. This article explains how to force Copilot to reply in a specific language using natural language prompts and how to verify the output is correct.
Copilot in Outlook uses large language models trained on multiple languages. It can generate text in dozens of languages regardless of your interface language. The key is providing the right instruction in your prompt. This article covers the exact phrasing to use, how to handle mixed-language threads, and what to do when Copilot ignores your language request.
Key Takeaways: Control Copilot Reply Language in Outlook
- Prompt prefix “Reply in Spanish” (or any language): Add this phrase at the start of your Copilot request to force the output language.
- Microsoft 365 admin center > Language & region settings: Changing your profile language does not change Copilot reply language; you must use prompts.
- Copilot pane > Draft with Copilot > Custom prompt: Use this option to specify the exact language when the default reply language is incorrect.
Why Copilot in Outlook Does Not Always Use Your Preferred Language
Copilot in Outlook determines the reply language based on two factors: the language of the original email and your Microsoft 365 account language setting. If you receive an email in English and your account language is English, Copilot generates the reply in English. If the original email is in French and your account language is English, Copilot may still reply in English because your account language takes priority.
The Copilot model understands over 40 languages but does not have a dedicated language selector in the Outlook compose interface. You must use natural language instructions in the Copilot prompt box. The model interprets phrases like “Reply in German” or “Write this email in Japanese” as direct commands. If you do not specify a language, Copilot falls back to the account language or the language of the last email in the thread.
One common misconception is that changing your Microsoft 365 display language or regional format will change the Copilot reply language. It does not. The display language only controls the Outlook interface, menus, and ribbon text. Copilot output language is independent of these settings. The only reliable method is to include the language instruction in your prompt every time.
Steps to Make Copilot Reply in a Specific Language
Method 1: Add a Language Instruction to the Copilot Prompt
This method works for any email reply. You add the language request directly in the Copilot compose box before generating the draft.
- Open the email you want to reply to
In Outlook, select the email and click the Reply button. The compose window opens with the original message quoted below. - Open the Copilot pane
On the Home tab of the compose window, click the Copilot icon. The Copilot pane appears on the right side of the screen. - Type your language instruction first
In the Copilot prompt box, start with the exact language phrase. For example: Reply in French or Write this reply in German. Then add the content you want Copilot to include. Example: Reply in French. Thank them for the meeting and confirm the date of March 15th. - Click Generate
Copilot processes the instruction and inserts a draft into the compose window. Review the text to confirm the language is correct. If not, click the back arrow in the Copilot pane and try again with a more explicit phrase such as Write the entire reply in Spanish only. Do not use any English.
Method 2: Use the “Draft with Copilot” Custom Prompt
If the default Copilot pane does not give you enough control, use the custom prompt option inside the Draft with Copilot menu.
- Click Draft with Copilot in the compose window
In the email compose window, locate the Copilot button on the top toolbar. Click it and select Draft with Copilot from the dropdown menu. - Choose Custom prompt
From the list of template options, scroll to the bottom and click Custom prompt. A text input field appears. - Write the language instruction and content
Type a prompt that includes the target language first. Example: Reply in Italian. Politely decline the invitation and suggest a reschedule for next week. Be specific about the language and tone. - Generate and insert
Click the Generate button. Copilot creates a draft in the language you specified. Review the draft and click Keep it to insert it into the compose window.
Method 3: Change the Original Email Language Before Replying
This method is useful when you want Copilot to match the language of the original email but the email is in a language you do not speak. You can ask Copilot to reply in a different language without changing the original email.
- Open the original email
Select the email in your inbox. Do not open the compose window yet. - Use the Copilot pane on the reading pane
With the email selected, click the Copilot icon in the top ribbon. The Copilot pane opens with the email context loaded. - Type a language instruction in the pane
In the Copilot prompt box, type: Write a reply in Portuguese. Thank them for the update and ask about the deadline. Copilot generates a draft based on the email content but in the language you specified. - Copy the draft into the compose window
Click the Copy button in the Copilot pane. Then open the Reply compose window and paste the text. You can edit the language or tone before sending.
Common Problems When Copilot Ignores Language Requests
Copilot Replies in English Even After You Asked for Another Language
This usually happens when the prompt is ambiguous. For example, Reply in French may cause Copilot to write the first sentence in French and then switch to English. Use a more restrictive prompt: Write the entire reply in French only. Do not translate. Do not use English anywhere in the reply. This forces the model to stay in the target language.
Copilot Uses the Wrong Dialect or Regional Variant
Copilot may generate European Portuguese when you need Brazilian Portuguese, or Mexican Spanish instead of Castilian Spanish. Include the regional variant in your prompt. Example: Reply in Brazilian Portuguese, not European Portuguese. Copilot understands these distinctions for major language variants.
Copilot Mixes Languages in the Same Reply
If the original email contains multiple languages, Copilot may mix them. Add a strict instruction: Use only Japanese in the reply. Do not include any English or other languages. If the model still mixes languages, regenerate the draft and add a negative example: Do not write in English. Write only in Japanese.
Copilot Language Support: Prompt vs Account Settings
| Item | Prompt-Based Language Control | Account Language Setting |
|---|---|---|
| Description | You type the language instruction in the Copilot prompt each time | Language set in Microsoft 365 account profile |
| Affects Copilot reply language | Yes, directly | No, only affects interface and spell check |
| Supports regional variants | Yes, if specified in the prompt | No, only base language |
| Requires manual input each time | Yes | No, but does not change Copilot output |
| Works for all supported languages | Yes, over 40 languages | Only languages available in Microsoft 365 |
The table shows that the prompt method is the only reliable way to control Copilot reply language. Changing your Microsoft 365 account language to French does not make Copilot generate French replies. You must include the language instruction in your prompt for every reply you want in a specific language.
Copilot supports the following languages: Arabic, Chinese Simplified, Chinese Traditional, Czech, Danish, Dutch, English, Finnish, French, German, Greek, Hebrew, Hindi, Hungarian, Indonesian, Italian, Japanese, Korean, Malay, Norwegian Bokmal, Polish, Portuguese, Romanian, Russian, Slovak, Spanish, Swedish, Thai, Turkish, Ukrainian, Vietnamese. For less common languages, test with a short prompt first to confirm the model can generate acceptable output.
To verify the language of a generated draft, you can copy the text into a translation tool or ask a colleague who speaks the language. Copilot does not display a language indicator in the compose window. The only confirmation is reading the generated text.