Hello Folks
I decided to begin learning the boehm Flute together with my Sister (she played Flute for a decade yet).
I want to play Celtic ornamentations for Instrumental Music ,which key system of the Boehm flute works best on that?
I’m new to the keyed flutes ,that’s why I’m asking here,up to now I only playde Keyless flutes or Flutes where the keys were extra and not the main notes.
Regards,Julian
Well, the Böhm flute has actually only one key system, which is called the Böhm system. 
There are some details (i.e. open “french style” key cups vs. closed cups, inline vs. offset), but the system is the same.
It is certainly possible to play irish/“celtic” music on the Böhm flute. There was a thread here on C&F not long ago where someone demonstrated it nicely. Joanie Madden also used to play the Böhm flute with Cherish the Ladies (though I don’t know if she still does). However, you’ll have a harder time with common ornamentation due to several crosslinks between the keys and some other quirks. That’s why most people use simple-system flutes, sometimes with additional keys.
Wo in NRW bist du denn? Ich komme aus Münster und spiele selber Flute, Pipes und Whistle. 
Faster than the fire brigade !!! 
Niederrhein ,north of Duisburg
She most certainly does still play Boehm flute (and with Cherish the Ladies).
No!
T. Böhm invented a flute mechanism which incorporated an “open” G# key (push to close), quite contrary to the currently more common French, “closed” G# key (push to open), and then there would be the Böhm originated difference in B and Bb thumb keys, please. That is, there indeed are differences in Böhm mechanisms. For instance, I play the original Böhm flute configuration, although perhaps my flute playing life could have been so much easier in terms of available flutes had I only learned to play on the more popular French, “closed” G# system, not that I have any regrets. Actually, I think Böhm did very well!