The size of the text and the font choice greatly impact the visibility and readability of an application. Additionally, your application also has to still be usable at high zoom levels.
Enlarge the application UI text by zooming up to 200%.
Is each text element and each image enlarged to double width and double height?
Is the text still readable (no overlaps)?
Are text alternatives for non-text content magnified in the same way?
Is the full content and functionality still available?
Does the layout still look OK?