Added "When to translate messages"

docs/internals/design-decisions.md

@@ -8,3 +8,7 @@ the core developers.
 1. **[When to support path aliases](https://github.com/yiisoft/yii2/pull/3079#issuecomment-40312268)**
    we should support path alias for properties that are configurable because using path aliases in configurations 
    are very convenient. In other cases, we should restrict the support for path aliases.
+2. **When to translate messages**
+   messages should be tralated when these are displayed to non-tech end user and make sense to him. HTTP status messages,
+   exceptions about the code etc. should not be translated. Console messages are always in English because of encoding
+   and codepage handling difficulties.