all the other languages state "the" fundamental natural science. Only German is "eine"...who's wrong ?

From a /language/ point of view, Japanese does not have clear equivalents of 'a' and 'the'. So if the German is translated from the Japanese it could be either.

However, if you consider the meaning of the sentence then it is clear that 'the' is appropriate. The terms 'natural science' and 'physical science' refer to the same thing - the sciences that deal with hard science. Chemistry, Astronomy, Physics, etc. As opposed to the so called soft sciences of Sociology, Linguistics, etc.

The important thing about that context is that physics can, in theory, be extrapolated to all the other hard sciences. Chemistry is about molecules and atoms, and and an understanding of physics lets you understand atoms and molecules (in theory, anyway). So, when it says Physics is the fundamental (or basic) physical science that is what it is referring to.

Yes, I got that, then I think German should be adapted. And I should change the French - translated from German - accordingly.

but can it not mean that among those, Physics is the fundamental one?

So I keep my french translation as is.
Danke sehr schön.

A translation?

Fixed?

Eventually, xtofu80 convinced me, so according to me, the German and French (which I translated from German) are right but the English and Esperanto are not.
The English should read "Physics is A fundamental natural science" and Esperanto "Fiziko estas fundamenta naturscienco."

but of course, there are also the indirect translations such as Russian that I cannot analyse...