Change the official language of Windows 7 as virtual machine
No, you cannot change this. Microsoft Windows exists in versions specific to languages and regions. If you have the French version of Windows 7 Professional, you cannot change its user interface language. You have to purchase a copy of the English version of Windows 7 Professional, delete your French copy, and make a new installation with the English version.

The alternative is to upgrade to Windows 7 Ultimate, which costs more money, and which can provide the user interface in different languages. The Microsoft Windows 7 Version Comparison Chart says that only Windows 7 Ultimate lets you "Work in the language of your choice and switch between any of 35 languages."

It goes without saying that Microsoft will only sell you Windows 7 Ultimate at the upgrade price if your copy of Windows 7 Professional is legally purchased and registered.