If you wish to install SMF and choose you preferred language, you can install it through our automatic script installation system - Softaculous. Here is the way of installing SMF from Softaculous:

cPanel --> Softaculous --> Forums --> SMF --> Install. Choose the preferred language from the Select Language drop-down menu.

The other way you can install SMF with additional languages on your SiteGround's account is to install in manually. If you want to perform a manual SMF installation and you do not know how exactly to do it, you can follow our detailed tutorial here:

http://www.siteground.com/tutorials/smf/smf_manual_installation.htm

Go to the link below and download the chosen language package:

http://www.simplemachines.org/download/?languages

Unpack the archive in the current SMF installation directory. Login to your SMF forum --> ADMIN --> Configuration --> Server Settings --> change your settings to the preferred language.