When installing the DHL Shipping module in Magento 2, this (or a similar) error occurs:
Interface 'Dhl\Shipping\Webservice\Client\GlRestClientInterface' not found
The required library "lib-shipping-mx" has not been installed together with the DHL Shipping module.
For the installation in Magento 2, it does not suffice to only copy the files of the DHL Shipping module into the Magento directory.
Install the DHL Shipping module as explained in the README.md in section "Installation instructions". This way, the required library will automatically be installed.