Cannot translate Shift_JIS into ASCII by Linguist

Linguist cannot translate Japanese Shift_JIS into ASCII correctly.

I wrote a simple test program named MyApp.exe to examine the issue.
The program has only one QPushButton in the MainWindow. The text on the button
is "ＣＬＩＣＫ" (this time I use double-wide uppercase alphabetical characters
included in the Japanese encoding in an easy-to-understand manner, since I
suppose probably you don't understand Japanese language).

When the button is clicked, a message box appears by the following code in
the slot function connected to the clicked() signal of the button.

QMessageBox::information(this, tr("ＴＩＴＬＥ"), tr("ＨＥＬＬＯ"));

In the body of main(), I wrote as follows.

QTextCodec::setCodecForTr(QTextCodec::codecForName("Shift_JIS"));

QTranslator translator;
translator.load("MyApp_en.qm"); // Fixed .qm file, since it's a test
a.installTranslator(&translator);

In the meantime, I added the following lines at the end of MyApp.pro.

TRANSLATIONS = MyApp_en.ts
CODECFORTR = Shift_JIS

Then, I generated MyApp_en.ts by typing as follows in the command prompt.

lupdate MyApp.pro

Next, I did translation by using Linguist as follows.

ＣＬＩＣＫ -> Click
ＴＩＴＬＥ -> Title
ＨＥＬＬＯ -> Hello

After that, I saved the translation result to MyApp_en.ts, and generated
MyApp_en.qm by [File]->[Release] menu of Linguist.

Then I activated the test program. As a result, the text on the button was
translated correctly. But the two phrases in the message box were not
translated, so row original phrases were shown ("ＴＩＴＬＥ" and "ＨＥＬＬＯ").

As a trial, I used lrelease command to generate MyApp_en.qm instead of Linguist,
then the following message was shown, although MyApp_en.qm was generated.

No QTextCodec for Shift_JIS available. Using Latin1

The translation result of that was the same as in the case of Linguist.

FYI: The system encoding of Japanese Windows XP is Shift_JIS, and VC++
accepts only Shift_JIS as Japanese encoding. Therefore, UTF-8 or any other
encodings than Shift_JIS cannot be used in my environment.