STR:
Settings -> Preferences -> General -> Localization: select a RTL language (e.g. Hebrew).
Restart NPP.

Result:
The tabs Close button is cut off by 1px.

Notepad++ v8.1.2 (32-bit)
Build time : Aug 3 2021 - 20:04:28
Path : C:---\notepad++ Original.exe
Command Line :
Admin mode : ON
Local Conf mode : ON
Cloud Config : OFF
OS Name : Windows 7 Enterprise (32-bit)
OS Build : 7601.23964
Current ANSI codepage : 1255
Plugins : ComparePlus.dll HTMLTag_unicode.dll MenuIcons.dll PythonScript.dll _CustomizeToolbar.dll