It needs C++ to create the widget that makes it, im also looking into how to do it since is way easier to stylize the font in an external program than to use the internal render of UE4, also for some fonts the engine deforms the font (i made an 8bit NES style font to test something and oh my, it looked like ■■■■)
The problem with the “new” way is that it is procedural at run time, which as good as it might look at any resolution, it has it own share of problems, you cant easily add letters with a typewriter effect and changing color of a single word, it needs the richtextblock, which adds a small space after closing the style word
You might have seen those already, but is the only thing i have found that talks about bitmap fonts, a plugin that is not available for sale and an old post about a plugin that couldnt be sold on the marketplace
https://forums.unrealengine.com/unreal-engine/marketplace/28407-umg-bitmap-fonts