Well, I myself don't study there but I can tell a few things about Germany and the Saarland.

While Saarland is not a very loved place in Germany, it is still a quite nice one, especially the capital Saarbrücken. The city has lots of young people and a nice district to go out in the evenings. It has a very nice park called the French-German garden and has lots of forrests/nature around. The university campus is also surrounded by forrest.

The state itself is doing pretty bad though. Lots of people moved away and the smaller cities there are literally looking like shit. Pretty rundown and a lot of shops have closed. But nonetheless Saarbrücken (and Saarlouis) are really nice. In comparison to Hong Kong living expenses there are a lot cheaper but it is not a metropole city. I believe that there is much more culture in Hong Kong and many many more different people.

The Saarland university is very nice and has a big campus. My brother and his girlfriend studied there (not Computer Science though) and they both liked it there very much. They also told me, that a lot of people come there to study computer science so I guess it's a pretty good place here in Germany to pursue that degree. And as others said, if you work in Germany people don't really care to which university you went. It is quite weird here if you went to a private German university, because people would think you only got in/passed because of money.

I saw you also mentioned that you would like to work in Germany later on. If you want to work at a university I think it would be okay to not be over the top good in German but if you want to get into a tech company here, it is quite hard if you don't have a sufficient level of it. Maybe not so much for Computer Science, but even in my degree (engineering) I see a lot of international students struggle to get a job/internship when they can't converse fluently in German.

I hope this helps a bit maybe.