Cyrillic contact name autocomplete fails in Cc after Reply all

Steps to reproduce

1. Have a contact in Nextcloud Contacts with a Cyrillic display name and a Latin email address, for example:
   • Name: Янковский Олег Леонидович
   • Email: yankovsky_ol@example.com
2. Open an email where this contact is one of the recipients.
3. Click Reply all.
4. Remove this contact from the To field.
5. In the Cc field, type part of the contact's Cyrillic name, for example янковский.
6. No autocomplete result is shown.
7. Type part of the email address instead, for example yankovsky.
8. The contact is shown.

The same contact can be found by its Cyrillic name:

• in the To field of the same Reply all composer;
• in the Cc field when composing a new message.

The problem only occurs in the Cc field after using Reply all.

Expected behavior

After removing a recipient from the To field, the contact should be searchable in Cc by its display name, in the same way as in a new message or in the To field.

Actual behavior

In Reply all, the contact is not found in Cc when searching by its Cyrillic display name.

Searching by the Latin email address works.

Mail app version

5.11.5

Nextcloud version

No response

Mailserver or service

No response

Operating system

No response

PHP engine version

None

Nextcloud memory caching

No response

Web server

None

Database

None

Additional info

No response

Start by reproducing the issue in the Reply all composer, focusing on the Cc field's autocomplete after removing the contact from To. Compare that behavior with the To field and a new-message Cc field using the Cyrillic display name; done means the contact is found consistently by name in all three cases, while email search continues to work.