I'm unable to add the word İskenderun to my user dictionary (en_US.usr). The word is highlighted as misspelled/unrecognized, but when I right click it,, nothing happens.

I've added dozens of other words without problems. I speculate the first letter, with the diacritical mark, might be the cause of the problem, but I have no idea how to fix it.

Here's my Notepad debug info:

Notepad v8.6.9 (64-bit)
Build time : Jul 12 2024 - 05:09:25
Path : C:\Program Files\Notepad \notepad .exe
Command Line :
Admin mode : OFF
Local Conf mode : OFF
Cloud Config : OFF
Periodic Backup : OFF
OS Name : Windows 10 Home (64-bit)
OS Version : 22H2
OS Build : 19045.4717
Current ANSI codepage : 1252
Plugins :
ComparePlugin (2.0.2)
DSpellCheck (1.5)
mimeTools (3.1)
NppConverter (4.6)
NppExport (0.4)