The admin (owner) of the account has access to the account's profile settings (accessible here) where the account's language can be changed. This setting applies to all campaigns and reports across your account unless you've manually set a different language for a specific campaign.
How to change your account-wide dashboard language
The admin (owner) of the subscription controls language settings.
To change your language, open your account settings control panel by clicking your user icon in the upper right hand corner of your dashboard. Then, click "Profile".
Alternatively, this may also be accessed through the sidebar by clicking on "Settings".
From the Settings page, select Company Details from the Account Section. On the next page, select your Language from the dropdown. Then, scroll down and save.
That's it! The dashboard will automatically reload, and your new language settings will instantly take effect.