Create a font from existing SVG icons
You can import svg files on the command line with the program birdfont-import:
A drawing saved as "a.svg" will be added to the glyph "a" when you run:
birdfont-import typeface.bf a.svg
A drawing saved as "U+62.svg" will be added to "b" when you run:
birdfont-import typeface.bf U+62.svg
You can import several files at once (on the command line) with wildcards:
birdfont-import typeface.bf *.svg
The proprietary version also has a pretty good batch import in the GUI. It looks like this:
Here are the details: https://birdfont.org/doku/doku.php/import_multiple_svg_files
There is also a functions in the proprietary version that makes it possible to center all glyphs vertically and horizontally with these buttons: