Separate support centers per language
If you have customers in multiple countries or want your support center available in different languages you can create multiple projects/workspaces for this, for example like we've done below.
In each of these support centers you will keep data and publish information in different languages, such as having a language specific start page for each language, have KB articles in different languages, discussion forums and so on...
You can then link to these support centers from your web site by using the different URL's in the "Project" --> "Support center" --> "Design" tab.
If you want you can join these projects/workspaces into a "unified support center" (in the "General" --> "Support center") the users can choose what language they will see in a drop down on top of the screen, as you can see below.
To handle issues/cases from all support centers centrally in one place the easiest way would be to do this by creating a filter where you show all the active issues/cases from your project and add this to your dashboard.
In addition to the setup above, you need to set the correct locale for the users that are created, this so that the system lables, buttons and headers are presented in the correct language.
One support center for all projects
In addition to having one project/workspace per language you can also have one central support center for all projects but this is more of a challenge and requires more work for you to configure
This requires that you do some programming and add the different languages directly into your support center (see "Project" --> "Support center" --> "Design"), and also that the support users have the correct Locale/language set in their user profile.
This also require that you have different data/info side by side in your support center, such as special forums, document/file structures, and different KB article structures.