By default, Subtitles downloads just one subtitles file in the first language it can find following the order you have set in your preferred languages. However, after subtitles for a video have been downloaded, you can click on the checkmark icon (✔) to view the details about the subtitle.
Then, click on the button which shows the number of results and Subtitles will all the available ones in your preferred languages.From here, you can download another subtitles file another language. This will overwrite the previously downloaded subtitles file with the one you've just selected.
Alternatively, Subtitles can also download subtitles files in several languages at once. To do so, first configure subtitles to append either the language code or the language name to subtitles filenames. This way, multiple files can be downloaded without overwriting each other.
After enabling a different naming style for subtitles, the setting named Download subtitles in all your preferred languages at once won't be grayed out anymore. Just click on its checkbox to enable it. With these options set, Subtitles will download a subtitles file for each one of you preferred languages.