I would like to hear notifications on my own language. And also would like the kids to know, when there is a leak of fire. Apparently it is possible with HA and it works grest.
Yes you can. There is a native google chromecast integration that uses TTS built into the hub. The HE supports many languages. There is also another custom integration for TTS, search our forums.
I use google minis for this. I think alexa also works
Do you know is there a possibility to use pre-recorded audios as notifications? For example I can download those same announcements from Google Translate. They come in mp3-format.
You can play an audio file directly. Stick it in the files section of your hub and then just address it directly as a playTrack url within a Custom Action to play it (hub_ipaddress/local/your_sound.mp3 should do the trick, as long as the device selected can play the file type).
Here's another example where I play sounds off a Raspberry Pi to a Google Nest Display for my alarm system (didn't get aorund to moving the sound files onto the hub), but it's the same process...