Non-ASCII fonts don't display in UMG

When using a non-ASCII language in the editor text in UMG will not display correctly.

Found in 4.23.1 CL#9631420
Reproduced in 4.24 CL#10053396, 4.25 Main CL#10050790

1. Open a project.
2. Change the Editor language to "Simplified Chinese".
3. Create a widget blueprint.
4. Drag a TextBlock onto the canvas.

Expected: The text displays normally.

Result: The text doesn't display the correct font.

Alternative, since we removed the translation.

1. Open UE4, any project.
2. Create a Widget Blueprint.
3. Add a TextBlock.
4. Add some Japanese text.