Problem with upload translation file in Azure AI Custom Translator

Question

Problem with upload translation file in Azure AI Custom Translator

George-Marius BACIU 0

Hello,

I am trying to use Azure AI Custom Translator. For this purpose, I have created a project and I tried to upload a dictionary file in xlf format. The upload fails and the error message is non-comprehensible.

Error_500_AzureCustomTranslator

I tried to select as a Child tag "Azure AI Custom Translator", nowhere to be found!

Where is the appropriate child tag?

Anonymous

2026-02-27T16:36:42.3733333+00:00

Hi George-Marius BACIU

Did you get any chance to review the above response.

Thank you!
George-Marius BACIU 0 Reputation points

2026-03-01T17:18:11.0833333+00:00

Hello,

Thank you for response. However, when I try the upload the translation file, I receive no dialog image to specify the child tag. I tried one more time, to be sure. The only thing requested is the uploaded file, that s all.
George-Marius BACIU 0 Reputation points

2026-03-06T19:57:35.7+00:00

Hello Sridhar**,**

Any feedback would be valuable, as your initial answer did not help me.
Manas R Mohanty 17,270 Reputation points Moderator

2026-03-18T05:05:09.7133333+00:00

Hi George-Marius BACIU

Manas here taking over the case now in absence of Sridhar.

Shall do replication and do the needful.

Thank you for your inputs.
Manas R Mohanty 17,270 Reputation points Moderator

2026-03-23T17:47:40.3366667+00:00

George-Marius BACIU

Good day.

I reviewed the case history.

It seemed the XLF /XLIFF input format is working at product group side.

Could you share your XLF file via DFM for review.

I have shared my thoughts on dedicated support ticket (10000 lines needed for finetuned translator model)

Suggested using Finetuning/Custom translator option from Azure AI foundry.

Hoping to connect with you once team's call to move towards case resolution.

Apologize for the inconvenience and delay caused.

Thank you.
George-Marius BACIU 0 Reputation points

2026-03-23T20:48:39.6333333+00:00

Hello,

Could you please share the DFM upload link for this case?

Regards

2 answers

Your answer

Anonymous

2026-02-27T16:36:42.3733333+00:00

Hi George-Marius BACIU

Did you get any chance to review the above response.

Thank you!
George-Marius BACIU 0 Reputation points

2026-03-01T17:18:11.0833333+00:00

Hello,

Thank you for response. However, when I try the upload the translation file, I receive no dialog image to specify the child tag. I tried one more time, to be sure. The only thing requested is the uploaded file, that s all.
George-Marius BACIU 0 Reputation points

2026-03-06T19:57:35.7+00:00

Hello Sridhar**,**

Any feedback would be valuable, as your initial answer did not help me.
Manas R Mohanty 17,270 Reputation points Moderator

2026-03-18T05:05:09.7133333+00:00

Hi George-Marius BACIU

Manas here taking over the case now in absence of Sridhar.

Shall do replication and do the needful.

Thank you for your inputs.
Manas R Mohanty 17,270 Reputation points Moderator

2026-03-23T17:47:40.3366667+00:00

George-Marius BACIU

Good day.

I reviewed the case history.

It seemed the XLF /XLIFF input format is working at product group side.

Could you share your XLF file via DFM for review.

I have shared my thoughts on dedicated support ticket (10000 lines needed for finetuned translator model)

Suggested using Finetuning/Custom translator option from Azure AI foundry.

Hoping to connect with you once team's call to move towards case resolution.

Apologize for the inconvenience and delay caused.

Thank you.
George-Marius BACIU 0 Reputation points

2026-03-23T20:48:39.6333333+00:00

Hello,

Could you please share the DFM upload link for this case?

Regards

Answer 1

Hi George-Marius BACIU

We got below review from product group.

Root Cause

The .XLF file contained <trans-unit> entries where <source> and/or <target> tags were present but had no text content. The upload service requires both tags to be non-empty and rejects files that fail this check. These empty tags are valid XML so they won't surface as a schema error, making them easy to miss without targeted inspection. Especially given the size of the file (Over 800,000 lines).

Resolution

Parsed the file programmatically to identify and remove all <trans-unit> entries with empty <source> or <target> tags. The cleaned file uploaded successfully.

The customer should ensure that the XLF files being uploaded in the future are formatted correctly and contains data in the source and target tag.

Status: working XLF file shared to customer via DFM

Thank you.

Answer 2

Hi George-Marius BACIU

When uploading an XLIFF dictionary to Azure AI Custom Translator, the portal prompts you to select a "Child tag" which identifies the XML element containing your phrase units. This isn't labeled “Azure AI Custom Translator”—you choose based on your XLF version:

For XLIFF 2.0 files (uses <unit> elements): choose unit as the child tag.
For XLIFF 1.2 files (uses <trans-unit> elements): choose trans‑unit as the child tag.

That ensures the upload parser recognizes and correctly interprets your phrase records

A few things to double-check:

File size : Custom Translator caps individual files at 100 MB. If yours is larger, split it into chunks or ZIP multiple sets.
Encoding/invalid characters: Remove any U+FFFD replacement characters—they indicate failed encoding conversions.
XLIFF formatting quirks: Ensure your <seg> and </seg> tags stay on the same line (no stray newlines). An extra line break inside a segment can break the parser.
Dictionary-specific checks

Phrase/sentence dictionaries require an equal number of source and target segments. Export each column to plain text to verify alignment before upload.

Supported language codes :

Both source and target codes must be supported. One side has to be en-US or en-GB.

If you’re still stuck, try uploading a small sample XLF (e.g. 10–20 entries) to see if it succeeds—this will help isolate whether it’s file size/format or something else.

Regarding the “child tag” on Microsoft Q&A:

after choosing the parent category “Azure AI,” type “Custom Translator” into the child-tag search box and hit Enter. If that doesn’t stick, you can also use the generic “Translator” tag—for this forum, “Azure AI Custom Translator” lives under the Translator category, not as its own first-level option.

References:

https://learn.microsoft.com/en-us/azure/ai-services/translator/custom-translator/concepts/dictionaries

https://github.com/MicrosoftDocs/azure-ai-docs/blob/main/articles/ai-services/translator/custom-translator/concepts/document-formats-naming-convention.md

I Hope this helps. Do let me know if you have any further queries.

Thankyou!