This old discussion related discussion
seemed to suggest that "realisation" and "Realisierung" often mean the same thing, but I don't feel comfortable about using "realisation" in some cases, and I'd like to see what others think.
The OALD entries which are similar to "Realisierung" are:
2 [U] ~ (of sth) the process of achieving a particular aim, etc. achievement: It was the realization of his greatest ambition.
4 [U, C] ~ (of sth) (formal) the act of producing a sound, play, design, etc.; or the thing that is produced
2. you can realise a dream, a vision, a victory, perhaps a project (in the sense of achieving it)
4. you can have a realisation of a concept: an idea is made real, usually in an artistic way. In management-speak, you can realise a product, meaning that you come up with an idea for a product and then turn the idea into the real thing.
Both of these uses are relatively rare (especially if compared to meaning 1 of "realisation", i.e. Wahrnehmung)
But what about:
We realised a study on XXX
12 realisations of the data are needed
Does that sound right to anyone?!