Since an update to MITK 2016.11 I cannot use special characters such as 'ä' or 'ß' when editing the name of a DataNode in Data Manager's tree view (via a double-click on the item or by pressing F2 when an item is selected). The in-place editor displays the correct characters, but they are not correctly transfered to the real node name (std::string). When the editor is closed, the characters are replaced by "missing character" symbols.
The reason seems to be a conversion of std::string to QString via QFile::encodeName() which is uses at least since https://phabricator.mitk.org/rMITK2a228d18dbe1e77560012e90954960690b953292
When I replace QFile::encodeName() by the more current QString::fromStdString() everything works fine for me.
Unless there is a good reason why QFile::encodeName() needs to be used, I suggest replacing it by QString::fromStdString(). See pull request https://github.com/MITK/MITK/pull/179