Are these languages applied only for the frontend or did you also add Arabic as a backend language? In order to translate any labels in Sitefinity you should have added a backend language (Basic Settings > Languages > Manage backend languages). Thus you will be able to add different versions of the label you need to change - see the attached image.
Once you have translated your message, it will appear localized to the frontend page when you are using the search result widget in different languages (please see the other attachments). For more information you could refer to our documentation related to Backend languages and labels
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Sitefinity CMS Ideas&Feedback Portal
and vote to affect the priority of the items