Issues in RTL GUI of Liferea itself only:
While the strings Feed: (ערוץ:) and Source: (מקור:) ARE appearing properly from Right-to-left, the strings Newsbin: (סל איסוף:), Folder: (תיקייה:) and Search Folder: (תיקיית חיפוש:) are still appearing from Left-to-right.
Newsbin: (סל איסוף:)
Search Folder: (תיקיית חיפוש:)
If you have made "Feed" and "Source" to appear appropriately, then it would not be difficult to apply the same thing to "Newsbin" "Folder" and "Search Folder"