Joe English tells us that, with 8.5, "the text widget uses TkFixedFont as the default font; which is the system-native fixed-width font. If you want the system native text font (which is what the entry, listbox, and a handful of others use) by default, then:
[text .t -font TkTextFont]
If you want the system-native "UI" font (used by buttons, menus, checkboxes, and most other UI elements): TkDefaultFont."