How to add new language and subtitles to a blu-ray?

[awiokz]

I'm a layman and I'd like to know how I can add a new language + subtitles to a blu-ray. I have a folder with the files of a movie, it contains "BDMV and CERTIFICATE".

[Ennio]

Subtitles on bluray are in PGS format, aka SUP. Together with audio & video, they are to be muxed into m2ts, which is located in BDMV\STREAM.
Reauthoring is required though.
With tsMuxer you can add SUP files and reauthor into a "movie-only" blu-ray.

[ChristianundCo]

years ago I added a pgs subtitle stream to a bd image. With mulitAVCHD

http://multiavchd.deanbg.com/

menu was kept, if you wanted to see the subs, you had to select them with "subtitles button" on remote control

but don't ask me about the way.

[Wenny]

You can use DVDFab's Blu-ray After Editor to add a new track or SUP/ASS subtitle stream to a bd image or folder and you will finally get a bd folder.
You can also set the delay time to ensure the synchronization among the track, subtitle and video.

https://www.dvdfab.cn/blu-ray-after-editor.htm