Before claiming that a function doesn't work, you should check what you're passing to it and what it returns, because it may be that the function is behaving just fine and the problem is elsewhere.

The Get­Current­DirectoryW function does not appear to support directories with Unicode characters in their names.

wchar_t currentDirectory[MAX_PATH];
GetCurrentDirectoryW(MAX_PATH, currentDirectory);
wcout << currentDirectory << endl;

The correct directory name is obtained if it contains only ASCII characters in its name, but it truncates the string at the first non-ASCII character.

If you step through the code in the debugger, you'll see that the Get­Current­DirectoryW function is working just fine. The buffer is filled with the current directory, including the non-ASCII characters. The problem is that the wcout stream stops printing the directory name at the first non-ASCII characters. And that's because the default locale for wcout is the "C" locale, and the "C" locale is "the minimal environment for C translation." The "C" locale is useless for actual work involving, you know, locales. You will have to do some language-specific munging to get the characters to reach the screen in the format you want, the details of which are not the point of today's topic.

In other words, the bug was not in the Get­Current­DirectoryW function. It was in what you did with the result of the Get­Current­DirectoryW function.

Here's another example of thinking the problem is in a function when it isn't:

The Set­Window­TextW function does not appear to support Unicode, despite its name.

wstring line;
wifstream file("test"); // this file is in Unicode
getline(file, line);
SetWindowTextW(hwnd, line.c_str());

If you look at the line variable before you even get around to calling Set­Window­TextW, you'll see that it does not contain the text from your Unicode file. The problem is that the default wifstream reads the text as an 8-bit file, and then internally converts it (according to the lame "C" locale) to Unicode. If the original file is already Unicode, you're doing a double conversion and things don't go well. You then pass this incorrectly-converted string to Set­Window­TextW, which naturally displays something different from what you intended.

Again, the point is not to delve into the intricacies of wifstream. The point is that the problem occurred even before you called Set­Window­TextW. The observed behavior, then, is simple a case of Garbage In, Garbage Out.

Here's another example from a few years ago.