@Vi42per Nice! I already converted the EN-DE from the same publisher. This one doesn't convert, though. That one was probably an older version. Odd that you have a mobi-format from 2016. Seems Kindle was using azw-format by then.
@Mandelgado58 This file is also a mess.
Would need a lot of extra work to convert. You're stuck with the string inflexions. However, you can download the xdxf-file, manually remove all those strings and convert it.