Yutaka Emura

No problem. For the rest of us, EmEditor already has a feature to auto-detect without displaying the result dialog box:

First, select Properties for Current Configuration (or All Configurations) on the Tools menu, select File tab, and check Detect All checkbox. Second, select Customize on the Tools menu, and clear Always Show Detect All Result checkbox. Now you can open a file with Auto Detect but without the Detect All Result dialog box.