Part-DB-server/config/routes/attributes.yaml

controllers:
    resource:
        path: ../../src/Controller/
        namespace: App\Controller
    type: attribute
    prefix: '{_locale}'

    defaults:
        _locale: '%kernel.default_locale%'
    requirements:
        # Match only locales like de_DE or de
        _locale: "^[a-z]{2}(_[A-Z]{2})?$"

kernel:
    resource: ../../src/Kernel.php
    type: attribute