Bug Report

I'll keep it brief – might hopefully save someones time. ;)

Translations folder in a theme – just as expected by load_theme_textdomain():

languages/
    theme-slug.pot
    de_DE.po
    de_DE.mo

CLI Command

wp i18n make-json languages/*.po --no-purge

The result

languages/
    theme-slug.pot
    de_DE.po
    de_DE.mo
    languages/de_DE-a0623ef93657e56554c5ddda522ed690.json

The translation will not load.
wp_set_script_translations() expects the file to live in {textdomain}-{locale}-{md5}.json.
After renaming it accordingly the translation loads.