Hi
I have an update regarding the Umlaut Problem. One of our server guys finally was able to solve the problem.
As it turns out the problem is related to Windows 10 (not really a surpise).
It may be solved by setting or appending an option for Java: -Dfile.encoding=UTF-8
In the command prompt (for a single session) you may use:
set _JAVA_OPTIONS=%_JAVA_OPTIONS% -Dfile.encoding=UTF-8
Or you may set an according environment variable in your Windows account.
By default Windows uses (at least on my machine) CP-1252 encoding. The used option forces the use of UTF-8 and the Umlauts are produced correctly on the client page 
.
Kind regards,
Vinz