[Feature Request] Preferred subtitle extension in current folder

[Cela]

Please add an option in Options -> preferences -> subtitles:
"Preferred subtitle extension in current folder"
and allow to choose and/or key-in the preferred subtitle extension.
Example:
Preferred subtitle extension in current folder: *.srt
or
Preferred subtitle extension in current folder: *.sub
etc.

Why?
Currently, BSplayer works as if it was set to:
Preferred subtitle extension in current folder: *.txt
Also see:
How to set preferred default subtitle file extension?

Thanks!