Ok, that's the solution: You take your desired hyphenation file from
https://github.com/onyx-intl/boox-op...onyx/data/hyph, place it in (newly created) folder /usr/share/cr3/hyph on your M92 and rename it to "Russian_EnUS_hyphen_(Alan).pdb". You might need ssh or serial connection to your M92 for this.
Unfortunately this solution needs some know-how. Would appreciate if somebody could give an easier solution, so that board members with less computer expertise can make use of this solution as well
(Make sure hyphenation is not disabled like explained in #4!)