I did some tests and seems that IE9.js and html5.js not solve the problem. However, I think I found the cause of it. I completely disabled the cache and I started to see the icon fonts without changing the icons.css file. It seems that the compressed css files are not properly read from IE8. However, sometimes some icons does not appear too, and when you install the simple messenger module disappear almost all the icons in the user menu. This is only an issue with IE8.

I also noticed that disabling see more the cache for html files solves the problem 'Correct the "New Display" list in the growth charts. It displays the lang key instead of name.'