You can create form questions and help text using those languages, but you cannot change default text for submit next, prev buttons, error messages, default "other" option in a dropdown. All those default text are tied to languages available in the language list.
When I try to write with e.g. Lao font in the form design, it does not work - only shows ......
I think you have to design the form in the 'old fashioned' way in Acrobat if you want to use special fonts, which means you must collect the data by email.
Designing the form in FormCentral and then transferring to PDF (for collecting by email and merging to a .csv table) has some other issues.
The Exported Values from multiple choice entries made in the FormCentral form are either 'yes' or 'off' in a separate field for each choice. Those field names does not include the text content of the choice, but only some strange program, maybe HTML, text.
In effect one has to go back to the form and find out what order the choice fields are, and then manually write the correct choice name into the field.
Seems that the FormCentral design function, smart as it is for online forms, is not really much helpful if you want to make a pdf form.
Or is there a function I have missed?