Hello Dominik

Thank you for your purchase.

You can change "Add New", "Edit" and "Delete" in /wp-content/plugins/wpdatatables/source/class.wpdatatable.php on lines 3426, 3430 and 3435:

array(
    'text' => __('New entry', 'wpdatatables'),
    'className' => 'new_table_entry DTTT_button DTTT_button_new'
),
array(
    'text' => __('Edit', 'wpdatatables'),
    'className' => 'edit_table DTTT_button DTTT_button_edit',
    'enabled' => false
),
array(
    'text' => __('Delete', 'wpdatatables'),
    'className' => 'delete_table_entry DTTT_button DTTT_button_delete',
    'enabled' => false
)

You're looking at the text in the brackets ('New entry', 'Edit' and 'Delete')

As for Print, you should go to lines 3302 and 3371 of the same file.

Please note that these changes will be overwritten when the plugin updates, so you will need to do it again.