Hi there,
I’m sorry to hear about the troubles with WooCommerce Admin plugin.
Our developers are aware of the translation issues and the progress can be tracked here:
https://github.com/woocommerce/woocommerce-admin/issues/2336
Regarding the orders that are not imported – the default job processing for ActionScheduler the import relies on uses WP-Cron to process the queues ( https://actionscheduler.org/faq/ ). So depending on your configuration and the number of legacy orders/customers to import, this could take quite some time to process.
You can also process the queues via WP CLI, which is massively faster, and would allow you to dedicate a specific server to run jobs if that would make the most sense for your environment, this is how the performance could be improved.