In German you can say something like 'I want this 2 times', meaning that you want 2 pieces of something. Is this correct in English to say, or is the equivalent rather 'I want 2 of these'?
(German here, so I know the original.)
No, you should not say "I want this two times".
It is simply not idiomatic in the sense it is used in German, a word-by-word translation doesn't work here.
You can say
I want this done (or other verb) two times / twice.
For items, you should stick to the simple
I want two (of these).
Note that you might also want to consider using expressions like
I'd like to...
instead of "want" - like in German, the politer phrase would be one avoiding a blunt "ich will".