How can I adjust / change the language? Why is the video in German even though I have my settings / profile in English? Are there subtitles?

At https://masterplan.com/user/settings you can switch the basic language between German and English.
Within each lesson, you can set the corresponding subtitles in many other languages to the right of the timeline under [CC].
 
Not every lesson is currently available in English and German audio.
I.e. if a lesson is only available in English audio, this lesson will also start with this language, despite your previous "German" setting.
The same is true for "English" to "German" lessons.

The flags also indicate the possible subtitles.
We are always in the process of gradually making our content available in different languages, both audio and text.
However, when and if the different additional dubbings will be available is not exactly determined.