Use External Font Icons in SAPUI5

1. Download font files. Those files have extensions like eot, svg, ttf, woff and woff2. Except the font files, normally there is corresponding CSS file in which icon classes are defined.
2. Create a new JSON file and give it a same name as the downloaded font file.
3. From the CSS file, find icon information. In CSS file, find code like
   "icon-abc:before{content:"\f0b4"}"
   If this icon is what you want to use in the UI5 app, then add an entry to the newly created JSON file:
   {
   "icon-abc": 0xf0b4
   }
4. Register it as a new font family by UI5 code:
   sap.ui.require(["sap/ui/core/IconPool"], function(IconPool){
     IconPool.registerFont({fontFamily: "NewIcons",fontURI: "/fonts"});
   }
   
5. Use the icon in UI5 view.
   <core: Icon src="sap-icon://NewIcons/icon-abc" />