Extension of "Tutorial:How to add new resource" mod by Kyoss.
Copper.jpg - See how it looks ingame
FontIconX.png - Image of new FontIcons file
I've expanded fonticons file to 256x512, making placeholders for a total of 253 glyphs.
CopperMod.zip - Contains adapted tutorial mod, adding copper to the game. Copy to your mods folder.
FontIconsX.dds.zip - Contains FontIconsX.dds, new fonticons file, copy it manually to Resource\DX9\ folder.
FontIcons.ggxml.zip - Contains FontIcons.ggxml which points to new fonticons file. This file should be copied over the existing file in Assets\DLC\Shared\UI\Art\Fonts\Font Icons\. If you don't have such folder, meaning you don't have DLC which adds stone, copy it to Assets\UI\Fonts\Font Icons\.
Keep in mind that you are overwriting the original game file, so backup the original file before overwriting.
FontIcons.psd.zip - Contains adobe project with new fonticons image so you can add your own glyphs for resources, religions, yields, or whatever (150 new glyphs can fit into FontIconsX.dds). I have used DXT3 format, but maybe some other format will get better looking icons.
I'm here to help if something is not clear.
Hopefully, Gods & Kings expansion will bring us modular fonticons, so it can be properly modded.
Have fun.