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Translating a customer email with AI? Back-translate it before you send.

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Translating a customer email with AI? Back-translate it before you send.
You can't check what you can't read. A common move is to paste the email, ask for Spanish and hit send. If you can't read Spanish, you can't tell whether the date, the refund or the apology made it through.

You can't check what you can't read

A common move is to paste the email, ask for Spanish and hit send. If you can't read Spanish, you can't tell whether the date, the refund or the apology made it through.

Translate it back, then compare. Translators have long checked their work this way: translate it back, then compare. WHO's protocol uses a back-translator who never saw the original and compares meaning, not wording.

Translate it back, then compare

Translators have long checked their work this way: translate it back, then compare. WHO's protocol uses a back-translator who never saw the original and compares meaning, not wording.

Source: WHO, WHODAS 2.0 Translation Package

The test email and the first prompt. Our fictional email tells Marta her walnut shelves can't ship before Friday, October 23, and offers an $18 shipping refund or a cancellation. This prompt turns it into Spanish.

The test email and the first prompt

Translate this customer email into Spanish for a customer in Mexico. Keep it warm and professional. Reply with the translation only.

Tested in GPT-5.5 (OpenAI API), Oct 2026

Our fictional email tells Marta her walnut shelves can't ship before Friday, October 23, and offers an $18 shipping refund or a cancellation. This prompt turns it into Spanish.

The round trip came back clean. In a separate call, the date, the $18 refund and the cancel option all came back intact. The one visible change was tone: “that's on us” became “we assume the responsibility.”

The round trip came back clean

Real output · GPT-5.5 (OpenAI API) · Oct 2026

…so we will not be able to send them to you before Friday, October 23. … Due to the delay, we will refund you the $18 of shipping as soon as your order is sent. If you prefer not to wait, you can cancel it and receive a full refund at any time before it is sent. … We did not keep you up to date as we should have, and we assume the responsibility.

In a separate call, the date, the $18 refund and the cancel option all came back intact. The one visible change was tone: “that's on us” became “we assume the responsibility.”

Then ask for a second opinion. Paste the original, the Spanish and the back-translation into this prompt. Part 1 compares the two English versions. Part 2 reads the Spanish the way the customer in Mexico would.

Then ask for a second opinion

Below are my ORIGINAL email, its SPANISH translation, and a BACK-TRANSLATION made in a separate chat. 1) List every place where the back-translation differs from the original in a promise, date, amount, condition or tone. Quote both versions. Say "none" if a category has no change. 2) Then read the Spanish as the customer in Mexico would, and list anything she could understand differently from what I meant (currency, dates, formality, idioms).

Tested in GPT-5.5 (OpenAI API), Oct 2026

Paste the original, the Spanish and the back-translation into this prompt. Part 1 compares the two English versions. Part 2 reads the Spanish the way the customer in Mexico would.

The round trip missed the real risk. “$18” comes back as “$18,” so the round trip can't flag it. In Mexico, $ is also the peso sign. The reader check caught it, plus a tú versus usted note.

The round trip missed the real risk

Real output · GPT-5.5 (OpenAI API) · Oct 2026

…In Mexico, “$18” can naturally be read as **18 Mexican pesos** unless the customer already knows the company charges in U.S. dollars. … …In Mexico, that can be fine for a friendly retail brand, but some customers may expect the more formal “usted” in customer service.

“$18” comes back as “$18,” so the round trip can't flag it. In Mexico, $ is also the peso sign. The reader check caught it, plus a tú versus usted note.

Source: Wikipedia, Mexican peso

What the check can and can't tell you. The round trip can catch a changed date, amount or condition, but not currency or formality. It's the same model family checking itself, so have a native speaker read anything with money or legal terms.

What the check can and can't tell you

The round trip can catch a changed date, amount or condition, but not currency or formality. It's the same model family checking itself, so have a native speaker read anything with money or legal terms.

Before you paste a real email. Remove names, account numbers and other personal details first, and check the tool's data policy or your employer's approved tools before uploading real documents.

Before you paste a real email

Remove names, account numbers and other personal details first, and check the tool's data policy or your employer's approved tools before uploading real documents.

Try it: Write “US$18” or your currency code before you translate.

Sources and assumptions

Assumptions:

The short version

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