Language subdomain not working on hosting

Hi everyone. I'm using CI 3.1.0 and modify output languages by subdomain. For example:

localhost:4001 for defaut language

en.localhost:4001 for english output

It woking good on localhost but recently when I upload the project to localhost, the main domain still working but when I enter the subdomain, it show

   

I have very little knowledge about hosting. So any ideas ?