No, you would need to set the database hostname as the server that it's on at Arahoster.
You can find this by going to the MySQL Databases icon within a package.
'localhost' generally means the MySQL databases are hosted on the same server as the websites, which is quite common in the web hosting industry with hosts that have a 'single-server' approach where all services run from the same machine.
It's different at Arahoster as we split all services and have a strict 'one server, one rule' policy.
At the Arahoster data centers, web traffic, MySQL traffic and storage are all physically different machines, so 'localhost' doesn't work.
