When translators and developers look at the same program, the see different things. For the developers, the code is clear. There is context around. For the translators, however, it is different. They just see the message text. It’s good to have a document that describes the two views.
Lasse Liehu has just finished a Techbase page about the subject. You can access is here: http://techbase.kde.org/Development/Tutorials/Localization/Message_Appearance .What I really like about this that it is full of illustrations. You can see the same situation from two viewpoints yourself. I recommend the example with “d/M/yyy”. That is a situation when
a context comment is really welcome.
I think this document is a must-read for both developers and translators. And if your program is not yet ready for translations, search Techbase for more documentation.