It sounds like you are running into an issue with encoding when trying to copy the XML code from a variable to a parameter in TestComplete. It's possible that the special characters in the "description" and "FN"/"LN" fields (such as "Ä", "Ö", and "Ü") are not being properly encoded or decoded when being copied to the parameter.
One solution to this could be to convert the XML code to a different encoding before copying it to the parameter. For example, you could try converting the XML code to UTF-8 or UTF-16 before copying it to the parameter.
Another solution could be to use a different method to copy the XML code to the parameter. Instead of copying the code directly, you could try serializing the XML code to a string, and then deserializing the string back into an XML object after it has been copied to the parameter.
Additionally, it would be helpful to check if you are using the correct version of TestComplete, as well as checking the log files for any error messages. if there is anything in the logging please place it here.