Broken in 18.3 and 19.5: Non-ASCII text in the "Button Value" field in the "Buttons and Forms" panel fails to export to interactive PDF.

To reproduce this issue:
1) Create a radio button
2) Add non-ASCII text to the "Button Value" field
3) Export to Interactive PDF
4) Look at the mouseover tooltip and see that the Button Value has lost any glyphs beyond U+00FF.

I've attached a PDF file demonstrating the issue.