To add a new language to an existing activity type, head over to the Control Panel, under the Data Types section, click on Manage Activity Types.
The list of existing activity types will appear, you can search for the activity type you want by scrolling through the list or entering the activity type name in the following field.
If you want to add a new language to an inactive activity type, click the Selected View field and switch to the view you want
Click the 'Pencil'-icon.
The following dialog will appear, click the Language field.
Select the language you want from the list.
After selecting a new language, you must enter the display name and other information for the activity type again in either the default or the new language.
Click the Update button.
Click the OK button, and you are done.
When the activity type is set to multilingual, a list of supported languages will appear as below.
Note:
1. Ensure that you are a User with 'Administrator'-rights set up to be able to access Control Panel.