If the subtitle language is not what you want, you can change the language abbreviation to you need.
for example, if the url web page is https://domain/en/youtube-to-mp3. you want to download the German subtitle of the video.
then you can input the web address of Browser with https://domain/de/youtube-to-mp3. de is language abbreviations of German.
of course, the video should have German subtitle itself. This subtitle detect is Only for youtube. Following list are language abbreviations.