Il est vraiment nice celui-là~!

This font would be awesome if you could make it letters too, so that like if you type in something like

"stop sign" stop would go where the bottom numbers are, , and sign would go where the top numbers are

The EAN (now GTIN-13) symbology only encodes numerics.
Note: The character sets appear to be 0-9 for L code words, a-j for R code words and A-J for G code words with -, : and ; for the various guard bar patterns.
See Wikipedia for the rules on generating a real symbol (they are somewhat complex).
Code UPC using six characters from the 'L' set and six from the 'R' set. Again, see Wikipedia for the checksum calculation.

Can you actually scan it and use it as a REAL UPC?