I installed ivona.tts_1.0.0.0c.apk. Created the directory ivona in android_storage. Then i copied the deu.deu.marlene directory into the newly created ivona directory. The following files are in this directory:
german.lex
lang_de_de.dat
libtiver.so
libttsivonavoice.so
libvoice_de_marlene.so
vox_de_marlene22i
The file lang_de_de.dat has to be renamed to lang_de_de_marlene.dat.
Open Android settings, got to System - Sprachen und Eingabe - Erweitert -Sprachausgabe. Selct Ivona TTS and click on the gear icon, this opens Ivona settings. Tap on Install voice data and see if it finds the files.
This works for me.
I’m not sure if i am allowed to share the files i used, but everything can be found here:
https://www.reddit.com/r/Android/comments/i3iaj6/ivona_tts_voices_for_android/