Steps to reproduce the issue

System - Manage - Language - Administrator - Set Russian language as default
System - Manage - Plugins - Search in plugin name

Test strings:

1. joomla
2. Joomla
3. пользователь
4. Пользователь

Expected result

1. All plugins with the word "Joomla" are shown
2. All plugins with the word "Joomla" are shown
3. All plugins with the word "Пользователь" are shown
4. All plugins with the word "Пользователь" are shown

Actual result

1. All plugins with the word "Joomla" are shown
2. All plugins with the word "Joomla" are shown
3. No plugins are found
4. All plugins with the word "Пользователь" are shown

System information (as much as possible)

Joomla 4.0.4

Additional comments

The problem may not only be with the plugin names provided the engine uses the same comparing string algorithm throughout the system.