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why Hebrew ascii codes are not accepted
Names must contain only ASCII letters (a-z-A-Z) digits (0-9), underscore, dot and dash.
Hebrew ASCII codes are from 128 to154.

You can set the validation pattern in the properties of the object.
See also the information about this in the help.

I haven't found where I can define "Validation pattern" in the properties.
Can you explain to me where and how?

I need to define ASCII code for all the website and not only for 1 object.
Where can I define ASCII codes for all my website?

You will need to do this for all signup objects individually.
However, normally a project only has one signup object anyway.