Yes, it's a simple choice during setup, and all menus, help, etc., become english.
Buy in Japan and you get a couple extra keys so that when you're composing or writing something you can easily switch between english & japanese input.
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That said, my wife got a Dell xps 15" last winter that I still think is a great machine. All the system is in japanese, but their help service is good and they might tell you how to change it.
If you get the english version, I think you have to install a language pack. Again, the j-version has an extra key to toggle easily between E/J.