We are creating English form. Our marketo language setting is Japanese and browser is Japanese as well.
Drop down area display Japanese character "選択" where it should be "Select" in English.
Is this "Select" text is browser driven?
Obviously, we don't want to display any Japanese in English form.
Have you tried to edit the values of the picklist?
Marketo forms don't dynamically adapt to OS/browser language. You have to build forms specifically to have this feature. I've written about this (at least a year ago, maybe) if you search the Community.