The rendering of multibyte characters in the prompt appears to have changed in recent versions and the characters are no longer rendered properly on my system.

Given the following command:

echo "Example content." | less --prompt "Example prompt ↓↑"

less v653 and earlier render the prompt as expected:

In v654, less started printing the code points in angle brackets with leading ^@ characters:

At some point this changed so the leading ^@ is now omitted in the current release version, v667, and the master branch, which currently print the code points in angle brackets:

When $LESSCHARSET is set to dos, the characters render properly, as illustrated in the following comparison:

echo "Example content." | LESSCHARSET=utf-8 less --prompt "Example prompt ↓↑"
# Example content.
# Example prompt <U+0086><U+0093><U+0086><U+0091>

echo "Example content." | LESSCHARSET=dos less --prompt "Example prompt ↓↑"
# Example content.
# Example prompt ↓↑

The system is running macOS 14.6.1 and the output of locale is:

LANG="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_CTYPE="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_ALL="en_US.UTF-8"

Thank you for developing such a useful and important program!