## Environment

OpenProject Begin of the insertion`17.4`End of the insertion Begin of the deletion communityEnd of the deletion with attachments on S3 storage.

## Steps to reproduce

1. Begin of the insertion End of the insertion Upload a UTF-8 text file containing non-ASCII characters Begin of the deletion like a `.md` or `.txt`
End of the deletion with accented characters) to a Begin of the insertionWP : `.md`, `.txt` or `.js`.

End of the insertion Begin of the deletion WP.
End of the deletion 2. Begin of the insertion End of the insertion Open the attachment inline, in the browser. Begin of the insertion


End of the insertion Begin of the deletion

End of the deletion ## Expected

The text is displayed with correct UTF-8 Begin of the insertion:
<img class="op-uc-image op-uc-image_inline" src="/api/v3/attachments/921417/content">End of the insertion Begin of the deletion (e.g. "métier").End of the deletion

## Current

Non-ASCII characters render incorrectly Begin of the insertion:
<img class="op-uc-image op-uc-image_inline" src="/api/v3/attachments/921418/content">End of the insertion Begin of the deletion (e.g. "métier" shows as "métier").End of the deletion

## Workaround

Right click + downloading the file and opening locally still works fine with Begin of the deletion
End of the deletion valid UTF-8.

## Notes

Binary attachments Begin of the insertionlike `.odt`End of the insertion Begin of the deletion (e.g. .odt)End of the deletion are unaffected since they are served as a Begin of the deletion
End of the deletion download by default rather than rendered inline.

The served Content-Type is text/plain without a charset, so the browser falls Begin of the deletion
End of the deletion back to legacy encoding. For S3-backed attachments the presigned URL sets Begin of the deletion
End of the deletion response-content-disposition but not response-content-type, so S3 returns Begin of the deletion
End of the deletion the stored content type without a charset.