Code 128 supports some ISO-8859-1 indeed, but it requires switching between encodings (there are 3 of them), and couldn't work with 128B (I guess the one used by the font, as it supports ASCII). See the table on Wikipedia: https://en.wikipedia.org/wiki/Code_128

actually it seems they support 128A 128B and 128C with the correct encoder.

  To use these fonts you have to use an encoder like the one below. It is an optimizing encoder, that means, it produces the shortest barcode that can encode the input. For this the encoder, if necessary or shorter, switches between the three available Code Sets (list from Wikipedia):
https://graphicore.github.io/librebarcode/documentation/code...