By default the size of the font in text chat in Skype is very small,but you can change the size and font type in skype easily.
To change the font size in Skype Open Skype window and go to the Tools menu and select Options,see the picture below ..
Select the font size and type of font you want and then press the OK button ,then press save button.
See the picture below ..
Will change the font size in text chat in skype.