From 2017, this was written by the late Dariush Maani who had a deep interest in Islamic mysticism. It focuses mainly on the Persian Hidden Words although it seems the author knew Arabic and English. It's quite an experience: the book jumps all over the place, non-sequentially. It appears to have been written in Persian, translated into German, then translated from German into English -- after the author's passing -- under the aegis of the NSA of Austria, and then typeset and printed in Spain! So, in addition to some unique insights, it has some irregularities.
Among the observations of interest, he equates "the three most holy words" of PHW No.19, "that true and radiant morn," [cf. Qur'an 7:172, re: the 'Day of Alast'], step-by-step, with a sequence in the Long Obligatory Prayer. Later he equates PHW No.29, "Out of the wastes of nothingness ...," with parts of the Medium Obligatory Prayer and the 'Tablet of Maqsud.' These are but two examples from this unusual book. Recommended.