Subtitle Editor is a capable video editing tool kit to transform, edit, correct, create or refine existing subtitles on GNU/Linux/*BSD. Based on GTK+2, It also shows sound waves, which makes it easier to synchronize subtitles to voices. You will not find too many capable applications in Linux that specialize in adding or editing subtitles. Three popular Linux video editors that let you work with subtitles are Avidemux, OpenShot video editor and PiTiVi. All three have more involved menus to handle a full line of video editing tasks. 
