Dark Mode doesn't work in latest version 1.18.4-Awesome-101. I think it is due to fact that it has been moved to Theme Settings which are unavailable for normal, non admin agents.

Using moon icon in the navbar redirects to the /index.php#behavior.

• osTicket-1.18.3-Awesome-104
• PHP 8.3.6

include/class.thread.php

class MergedEvent extends ThreadEvent {
function getDescription($mode=self::MODE_STAFF) {
return sprintf(
$this->template(
__('{somebody} merged this ticket with %s{data.id}%s{data.ticket}%s {timestamp}'),
$mode
),
'', ''
);
}
}

Stack trace points directly to the sprintf() call.

Root Cause:
The {somebody} placeholder is expanded before sprintf() is executed.

In our installation the merged event was created by an agent named:

Casper F. Sørensen

The generated HTML contains an avatar URL with URL-encoded characters:

name=Casper+F.+S%C3%B8rensen

After placeholder substitution, sprintf() receives a string containing:

%C3%B8

PHP 8 interprets "%C" as a format specifier and throws:

ValueError: Unknown format specifier "C"

This causes the entire ticket thread rendering to fail.

Example Debug Output:
Template result:

<img class="avatar" ... name=Casper+F.+S%C3%B8rensen" />Casper F. Sørensen
merged this ticket with 344
Ticket #S416

Expected Behavior:
Merged ticket events should render correctly regardless of agent names containing non-ASCII characters such as:

ø
æ
å
ü
é
etc.

Actual Behavior:
Ticket thread rendering fails with a fatal PHP error.

Suggested Fix:
Avoid using sprintf() after placeholder expansion.

One possible approach:

Build the link placeholders before template rendering.
Use str_replace() instead of sprintf().
Escape literal percent signs before passing strings to sprintf().

For example:

return str_replace(
array('LINK_START', 'LINK_MID', 'LINK_END'),
array('', ''),
$this->template(__($raw), $mode)
);

Impact:
Any merged ticket can become unreadable when the merge event was performed by an agent whose display name results in URL-encoded percent sequences being present in the rendered HTML.

This appears to be a PHP 8 compatibility issue rather than a localization or theme issue.