Not sure that you can change the size of the fonts. It's not related to the UI per say it's part of the game.
A general rule for whether or not you can do some window in the game would be...1) Can you remove it? 2) Would the game still run without it? 3) Would the game still be functional without it?
Answering no to any question would most likely give you an answer to whether or not it could be modded. My thoughts are that you can't change the size (it's hardcoded into the game), but I could be wrong...
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