First Character of Chinese or other multi-bytes characters display name

[mio-19]

⚠️ Before posting ⚠️

• This is a bug, not a question or an enhancement.
• I've searched for similar issues and didn't find a duplicate.
• I've written a clear and descriptive title for this issue, not just "Bug" or "Crash".
• I agree to follow Nextcloud's Code of Conduct.

Steps to reproduce

1. Set display name to Chinese or other multi-bytes characters
2. See the error. It is intended to show the first character. But it is displaying a square.

Web and Android:

Expected behaviour

First character

Actual behaviour

square

Android version

14

Device brand and model

Samsung S23

Stock or custom OS?

Stock

Nextcloud android app version

3.29.0

Nextcloud server version

Shouldn't matter

Using a reverse proxy?

Yes

Android logs

No response

Server error logs

No response

Additional information

No response

[AndyScherzinger]

Avatars are generated server side, so moving the issue to the server repository.

[mio-19]

#42534