Fix npp displays Chinese characters in traditional characters in DirectWrite render mode since version 8.6

Yan Serenade

Since Notepad++ 8.6 added DirectWrite as the default rendering method, the program displays Chinese characters in traditional characters, and modifying to GBK font cannot fix the issue; reverting to GDI rendering resolves the problem.

I tracked the issue:
According to Scintilla’s description, DirectWrite determines which set of glyph variants to use for CJK characters based on localeName (locale name).
The default values for Scintilla (see Platform.h) are:

constexpr const char *localeNameDefault = "en-us";

The repair method is as follows:
After enabling DirectWrite, the correct font locale will be automatically set according to the system locale in the init method:
Taking the notepad-plus-plus-8.9.2 source code as an example, modify the if statement starting from ScintillaEditView.cpp:482 to the following:

		// === New: Automatically set font locale based on system locale, and fix the issue with CJK font selection ===
		wchar_t sysLocaleName[LOCALE_NAME_MAX_LENGTH] = { 0 };
		if (GetUserDefaultLocaleName(sysLocaleName, LOCALE_NAME_MAX_LENGTH) > 0)
		{
			int len = WideCharToMultiByte(CP_UTF8, 0, sysLocaleName, -1, nullptr, 0, nullptr, nullptr);
			if (len > 0)
			{
				std::string localeUtf8(len, '\0');
				WideCharToMultiByte(CP_UTF8, 0, sysLocaleName, -1, &localeUtf8[0], len, nullptr, nullptr);
				localeUtf8.resize(len - 1);
				execute(SCI_SETFONTLOCALE, 0, reinterpret_cast<LPARAM>(localeUtf8.c_str()));
			}
		}
		// === New end ===

After DirectWrite initialization, this code reads the user’s system language (such as zh-CN) and notifies Scintilla to use the corresponding font variant through SCI_SETFONTLOCALE. This ensures that the Simplified Chinese system (zh-CN) correctly selects the Simplified Chinese font, while the Traditional Chinese system (zh-TW) selects the Traditional Chinese font.
Finally result：

rdipardo

Bravo!

You may also be interested in this issue: “ANSI auto-completion shows garbled text when typing Chinese characters (since v8.8)”

Yan Serenade

@rdipardo In Version 8.9.3, The program behaves correctly.

xomx

@Yan-Serenade

https://github.com/notepad-plus-plus/notepad-plus-plus/issues/16719#issuecomment-4132203721