How can I automate the subtitle adding process in FFMPEG?

Question

The situation is, that I have 10 MP4 videos and a folder for each of them that has the same name as its video. In each of folders there are around 30 SRT files I need to add. I would like to automate this. I mean a script that would add each SRT file to the video and add the correct handler for the subtitles, so that the subtitle would appear as "English" instead of "Subtitle #12" in a movie player. I made a python script; it's far from perfect and it does not add the handlers correctly.

The name of each SRT file is something like "20_Hebrew.srt"

import os
file_dir = r"Path/to/my/files"
sub_dir = file_dir + "/Subs"


def add_sub(file, file_name):
    cmd = f"ffmpeg -i '{file}' "
    sub_list = []

    no_extension = file_name.replace(".mp4", "")

    for sub_name in os.listdir(sub_dir + f"/{no_extension}"):
        s = os.path.join(sub_dir + f"/{no_extension}", sub_name)

        if os.path.isfile(s):
            cmd += f"-i '{s}' "
            sub_list.append(s)
    
    cmd += "-map 0:v -map 0:a "

    for i, v in enumerate(sub_list):
        cmd += f"-map {i+1} "
    
    cmd += "-c:v copy -c:a copy "

    for i, v in enumerate(sub_list):
        sub_lang = v.replace(".srt", "")
        index = sub_lang.index(f"/Subs/")
        sub_lang = sub_lang[index:]
        index = sub_lang.index("_")
        sub_lang = sub_lang[index+1:]

        cmd += f"-c:s:{i} mov_text -metadata:s:s:{i} language='{sub_lang}' -metadata:s:s:{i} handler='{sub_lang}' "

    cmd += f"'{file}_OUTP.mp4'"

    os.system(cmd)

for file_name in os.listdir(file_dir):
    f = os.path.join(file_dir, file_name)

    if os.path.isfile(f):
        add_sub(f, file_name)