This layout contains the texts in Italian but the layout is in English. Can I change the language of defaut in English or do I need to replace the contents in English and translate?
The important thing is that the language of content needs to be correctly set.
If you create the Layout in English then WPML will understand it to be English and use it on English posts/pages. You can translate it to Italian (as shown in your screenshot) if needed.
But, say, your Layout is English, but you added some Visual Editor cells to the Layout and you have entered text in those, and the text is in Italian.
That's okay, as long as you tell WPML that the text is Italian (it will assume it is English).
Go to WPML > String Translation and find the text you added. In my screenshot I had just added some text in English, but if I had added it in a different language I could select those texts and then use the "Change the language of the selected strings" button to tell WPML that they were not English.