And if all of that does not work you can actually add multiple libs at a time with the library management tool. Use the button for browsing for libs to add, and in the file browser like tool that opens you can use the shift and control keys for multi selection.
More details see Library management in KiCad version 5 (Section Adding a library to a library table) Be aware that the graphical interface might have changed slightly but the general functionality is still the same.