Please fill out the fields below so we can help you better. Note: you must provide your domain name to get help. Domain names for issued certificates are all made public in Certificate Transparency logs (e.g. crt.sh | example.com), so withholding your domain name here does not increase secrecy, but only makes it harder for us to provide help.
You cannot get a cert from Let's Encrypt for "localhost" as it is not a domain name in the public internet. And, you won't be able to satisfy an HTTP Challenge on port 8080.
But, if you can explain more about what you are trying to do we can probably help. At least explain what you want the cert to do.