The IPS Community Suite is installed with an English language pack which is also set as the default. However, you can set another language as the default language if you wish.
Note: The IPS Community Suite attempts to determine the correct language for a user based on information their browser provides. If this can be determined, and you have an appropriate language pack installed, then providing the user hasn't specifically chosen another language, that language will be shown to them regardless of your community default.
To set the default language, navigate to Customization -> Languages in the AdminCP, and click the Edit icon next to the language you want to set:
In the popup window that appear, check the Default Language option, and save the form.