Another open-source, GPL licensed subtitle manager is Subtitle Workshop. This one features a user-friendly interface that is available in multiple different languages. Its tools for timing and text manipulation are customizable so that you can create an interface that allows you to operate in the workflow that is most convenient for you.
Subtitle Workshop will allow you to quickly set durations, adjust lines, check your spelling, and automate frames per second changes. It allows you to detect, mark, and fix timing or text errors using a comprehensive set of automatic and manual tools. It can also be extended using Pascal script files.