Aegisub

Originally created as a tool to make typesetting, particularly in anime fansubs, a less painful experience, Aegisub has grown into a fully fledged, highly customizable subtitle editor.

It features a lot of convenient tools to help you with timing, typesetting, editing and translating subtitles, as well as a powerful scripting environment called Automation (originally mostly intended for creating karaoke effects, Automation can now be used much else, including creating macros and various other convenient tools).

This is an unofficial snap, the developers may not be responsible for any bugs in it. For any bug reports: https://github.com/vcprocles/aegisub-procles-snap

NOTE: Default Automation scripts are located in a read-only location, thus you need to run aegisub-procles.move-script to create a user-writable version of the script directory and then change the settings accordingly.
Channels: stable - last version from new maintainers
candidate - older version, most of the changes are to make this build on newer systems
beta - older version with some more Automation plugins built-in, functionality not guaranteed