I write this answer as it might help someone in the future – this is slightly weird. My Apple account is created in the USA, so, I assumed if I changed that to Germany, it will surely work out. This turns out not to be true.
Then I used the link posted an earlier answer for the iOS German ALDI talk app. The link is here and I was not able to open it in the iPhone app store and it provides the message as the app is not available in my region or country. Mind it the iTunes account is set to Germany at the time. I don’t get this.
Finally, I did a Google search and ended up in the page
Chip.de. The page link is provided here.
I clicked the link and it downloaded and opened the same German app provided earlier. This time I was able to install it in the iPhone and rest of the process went seamlessly.
The app has a rating of 2.5 but it works just fine. Only the process of installation is not very convenient.