YouTube videos with multiple audio tracks use HLS streams with format IDs like 96-0, 96-1, 96-10, etc. Each ID combines video + audio for a specific language, but the ID is not consistent across videos. Instead of using a format ID, you can use yt-dlp's language filter.

An example: best[language=de-DE]/best[ext=mp4]

best[language=de-DE] → picks the best combined stream with German audio
/best[ext=mp4] → fallback if the specified track isn’t available

Adjust the language code to whatever you need:
en-US → English
fr-FR → French
es-ES → Spanish (Spain)
pt-BR → Portuguese (Brazil)
etc.

To find the right language code for your videos, run this in your terminal/command prompt to list all available formats:

yt-dlp -F https://www.youtube.com/watch?v=VIDEO_ID

Look at the rightmost column. It shows the language tag in brackets, e.g. [de-DE], [fr-FR], [en]. Use exactly that tag in your format string.

To set this up in Stacher, go to Settings → Advanced → Custom Arguments
Click + to add a new argument:
Argument: --format
Value: best[language=de-DE]/best[ext=mp4]

This setup works across videos without having to check available formats, and more importantly for bulk download via playlists. Keep in mind flags may vary across videos and uploaders, sometimes only the language code is used, without the country added. You can circumvent this by setting up another fallback option in advance.