Eclipse Plugin Development: German Umlauts stored as UTF8 showing up wrong in SWT controls but correct in String constant - eclipse

Question

I am writing an Eclipse Plugin. All my source files are encoded as UTF8 (Alt+Enter shows "Text file encoding: UTF8").
When I run my plugin using "right click -> Run as eclipse application" everything works fine.
However, when I install my plugin using an update site in another (but identical, i.e., copied) Eclipse application, German Umlauts (Ä Ö Ü...) get messed up in all SWT-controls, but not in String constants.
Example:
public class MyWizard extends Wizard{
public NewEntityWizard() {
super();
setWindowTitle("This will NOT work: Ä");
}
public void foo() {
String contents = "This WILL work: Ä";
ByteArrayInputStream stream = new ByteArrayInputStream(contents.getBytes());
// write stream to file test.txt
}
The window title will show up as: "This will NOT work: ä"
When opening the file test.txt in Eclipse, with UTF8 encoding, it will contain the correct test: "This WILL work: Ä"
Both will work when run by using Run as, i.e., when not installing the plugin.
How do I resolve this?
I figure, the compiled plugin / bin files might (correctly) be encoded in UTF8, but read in a different encoding by the second Eclipse installation. If so: How do I tell the JVM / Eclipse to read the Plugin's bin files in UTF8?
Any help is appreciated.

Answer 1

Solved the problem myself. The issue was a Bug in Eclipse (I am running Oxygen, not sure if the problem exists in other versions).
The bug was, that the PDE Builder, which builds the product, does not respect the encoding settings configured in Eclipse. It uses the default encoding of the plattform, which is not UTF8. This seems to be a Windows only problem. The java builder does not suffer from this bug, that's why the problem did not occur during testing.
Bug Description:
https://bugs.eclipse.org/bugs/show_bug.cgi?id=516656
Solution:
As workaround I added the following line to the eclipse.ini of the building Eclipse installation, build the product again and installed it again. The setting makes UTF-8 the default encoding for the whole VM.:
-Dfile.encoding=UTF-8
This solved the issue.