Custom font issue

When you export a font using FontBuilder or something else, you have a binary file.
Using binarybuilder, you transform this binary file into a cpp/h pair.
You can use those to embed your font in l+f, as a typeface, via the getTypefaceForFont() function in l+f.

Now, how can you tell to set it in bold or italic ?
What have I done wrong ?

You can’t set it to bold or italic. If you need a bold font, embed a bold version as well, and use that.