I found now a solution, that works great :) "With[...]" does exactly what I was lookiing for:

test[inNumber_] := Module[
   {outNumber, outMathematica, outLatex},

   outNumber = inNumber^2;
   outMathematica = SuperscriptBox[inNumber, 2];
   outLatex = StringJoin["$", ToString[inNumber], "^2$"];

   With[{outButton = outLatex},
    Print[Button[DisplayForm[outMathematica], Print[outButton]]]
    ];

   Return[outNumber];
   ];

@Kuba: Sorry, I didn't explain well my problem before. I didn't want to have dynamic content in the Button, only the content of a local variable at one time. But thx for the hints. My english is really bad, so its not so easy for me to say what I want to say ;)

The little program was just an example. You changed in way, that doesnt answer my question. The two variables in Button are both local defined. If possible, this shoudnt be changed. But if there is no such solution, I put the value of the local "zahl2" in the global "zahl3", then it works.

test[zahl_] := Module[
   {zahl1, zahl2},

   zahl1 = 5;
   zahl2 = 10;
   zahl3 = zahl2;

   Print[Button[zahl1, CopyToClipboard[zahl2]]];
   Print[Button[zahl1, CopyToClipboard[zahl3]]];

   Return[zahl];
   ];