You can specify whether you want a Text part, or other part that accepts user input, to only accept single-byte or double-byte characters. Open the settings for the Window part and look at the following properties:
You can require all input fields in a window to accept a certain of input by setting values for these properties. Or, you can require entry of a certain type of input on a per field basis by connecting the gettingFocus event of the data entry part to a script such as the following:
focusText
"Assumes you want the Text1 part to require double-byte phonetic data entry"
(self subpartNamed: 'Text1') primaryWidget shell
inputMethodEditor: true;
inputType: XmDBCSPHONETIC;
romanInput: true.