You can apply the language packs to an account in three different ways

Option 1:
Click on Accounts on the left hand toolbar and choose accounts of a particular type.
Click on Apply Language Pack. Choose the applicable pack and click on Apply.

Option 2:
Click on Accounts on the left hand toolbar and click on the account to view its sub-accounts
Select the sub-accounts that you want to apply a language pack to.
Click on Apply Language Pack. Choose the applicable pack and click on Apply.

Option 3:
Click on Accounts on the left hand toolbar and click on the account to view its sub-accounts.
Click on the sub-account that you want to edit.
Click on Apply Language Pack. Choose the applicable pack and click on Apply.
Click on Submit at the bottom of the form to update your sub-account