I actually does not matter where you launch Developer from. You can launch from wrapper or from Start Menu -> PROGRAMS -> InstallShield -> AdminStudio Tools -> Developer.
Also since your machine is German NT4, and if you do not have German language pack for Developer follow this steps. You do not need do this if you have German language pack for Developer installed.
(I presume the legacy application you are repackaging is English)
1 Once the repackage is done. Open the .inc file in the notepad.
2 Look for OSInfo line
OSInfo('Windows 2000','5.0.2195 ','?','?').
3 Replace this with following line
OSInfo('Windows 2000','5.0.2195 ','1033','1033'). The 4th and 5th parameter are the Local Id's for your machine and language. They need to be replaced with locale id's for English.