This page is set up as test for Vimeo

On our site we have dozens of pages, each with a dozen links to videos on vimeo. Each of these pages is in the language of the readers (participants to our courses)
We have created subtitles in multiple languages for the videos. And I would like the language of the page (=language of the user) to be automatically appearing when playing the video.
It works with the variable texttrack=es. However the formatting of the subtitles then dissapears.

Watch these videos:

In this video the language is not pre-selected. The user can play it, then select a language and all works fine.
The subtitles appear with the format I have set in the Vimeo dashboard.

In this video the language is pre-set to Spanish. The subtitles do appear, but now the formatting of the subtitles has disappeared. and it is white text on a black background.