Maybe someone will find helpful what I did with my notifications:
- Downloaded mp3 of notification sound which will be at the begining of the voice message (https://notificationsounds.com/notification-sounds)
- Downloaded mp3 of voice message for certain action for example "garage opened" in my language (https://freetts.com)
- Joined both mp3 files in to one mp3 (https://clideo.com/merge-audio)
Now I have notification files with voice message customized for every action... (ex. garage opened / closed, wash machine finished...)
For all other notifications I just I use file downloaded in step 1.