TTSMaker (Free Text-to-Speech)
A free tool that reads text aloud in a human-sounding voice and turns it into an audio file. It offers many languages including Korean along with a range of voices, and states that the generated audio can be used commercially.
How to try it
Choose Korean (or another language), pick one of the listed voices, type your text into the box, and press convert to generate the audio. You can download the file or export SRT subtitles, and insert pauses with notation like ((⏱️=1000)). The free tier allows 20,000 characters per week, and generated audio is deleted automatically after 30 minutes, so download it right away. Korean is supported.