The field mapping only affects new controls dropped onto a form. You can write a program that can go through and change the class and classloc fields of the forms to change them. Make sure you make a backup first though.

>When I use textboxes and label in my form, preferred language is not English. How can I set a newly-created textbox or label in my preferred language. I try to edit "Tool" - "Option" - "Field mapping", but it doesn't work (I created a Thai-textbox class and map Textbox to the class).