Hi Matthias,
Can you produce the problem on demo.mojoportal.com?
I just tried it there and it worked for me. I created a style named highlight for element span and class highlight. I then select some text in the editor and click the styles dropdown and chose my style highlight and it wraps the text in a span with class="highlight" just as it should.
Note that it does work different in CKeditor than in TinyMCE, the options you see depend on what you have selected in the editor. For example if you define a style for img element it will only be available when you select an image in the editor.
Is it possible to load the former version of TinyMCE to solve my problem?
What do you mean? You can use TinyMCE if you don't like CKeditor and you can insert € from the toolbar in any of the editors.
Hope it helps,
Joe