Here is how you can fix this on your end:
1. Open the Project manage (6.1 or the version your project is in) and create a new project
2. Login to the backend of the new project and export its language pack (the English one)
3. Download the language pack already provided in this thread (the old one).
4. Scroll to the bottom of the downloaded language pack where you can see the entries for the RadAsyncUpload
5. Copy them over to the pack you have exported from the clean/new project and save.
6. Import the renewed language pack into your project
7. Restart the application
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 Public Issue Tracking
system and vote to affect the priority of the items