Editing resource properties files in Eclipse is easy - as long as you don't need characters beyond the ISO-8859-1 encoding.
Characters that cannot be directly represented in this encoding can be written using Unicode escapes.
I really don't know all Unicode escapes for german umlauts and I don't want to waste my time with those things when editing properties files.
The first solution I tried was to create my properties file with an UTF-8 encoding using Notepad++. This works pretty well as far as you don't touch this file ever again with Eclipse :-(
Any change of the file using Eclipse converts this file back to
ISO-8859-1 encoding and native umlauts like "ä" and "ü" will display
strangely in your application.
Note: In Eclipse Preferences every encoding setting (Workspace, CSS, HTML, JSP, XML) was set to UTF-8. In this Stackoverflow question someone tried even the option of specifying -Dfile.encoding=UTF-8 in eclipse.ini. Still not working.
BTW, if you prefer creating and maintaining UTF-8 properties files (maybe you don't work with Eclipse or use another IDE/Editor which is capable of editing UTF-8 property files) you have to check out this stackoverflow posting. Both code examples of reading resource bundles in UTF-8 format work like a charm.
For me, this is not an option because I want to stick to Eclipse and I don't want to edit the properties files with a different tool.
What finally really did the trick was the Resource Bundle Plugin for Eclipse mentioned in this stackoverflow answer. The plugin converts native non ISO-8859-1 characters on the fly to Unicode escapes and frees you from typing the Unicode escapes manually.
All in all a pretty good solution and a very handy plugin.