Pretty much all german airlines require more than a basic command of the german language although basic german could be enough to just get in if you promise to speak it fluently within a month or so.
Taxation is indeed high with a max tax level of 45% if you earn more than 250.000€ a year, which you won't with CLH, 42% below that. But that is only half of the story since you need to pay a lot for social security and medical insurance so expect to lose around 58% of your income. Average state rate is 54% in germany which is the second highest worldwide (right behind Belgium), however since you earn way over the average wage you will pay a bit more.
Apart from that is Cityline a pretty good employer, especially for the kind of equipment they fly and there is a chance to join mainline Lufthansa later on. However if you can get into Cityline you can go directly into mainline at the moment, which is quite a bit better.