At first glance, it looks like FontForge doesn't support OpenType Collection font format (OpenType PostScript collections). It can, but the UI doesn't make it obvious on how to do this.

UI Changes needed:

• Rename "Generate TTC..." to something more appropriate. ("Generate Collection...", maybe?)
• Add "OpenType (OTC)" to the font format selection menu.
• (minor) recognize otc files as a font file in the open dialog, including icon.