Yii core messages refer to static text strings in the core Yii framework code which are meant to be displayed to end-users (e.g. core exception messages, default validation error messages). Customization of these core messages is needed in two circumstances:
As you know, the CDetailView widget displays details of a single model. If no formatting is specified, boolean values that are stored in the database as 0 and 1, are represented in the detail view as 0 and 1. If formatted as boolean, they are represented as 'No' and 'Yes'. We want to add i18n support, so that Yes and No appear in the current language.
Sometimes you want to use exisiting translations for locales, which do not directly match.
An example would be a website targeting Germany (de_de), Austria (de_at) and Switzerland (de_ch, fr_ch, it_ch). Although you may have
exisiting translations for German (de), French (fr) and Italian (it), there are problems using it directly.
The giix code generator has out of the box i18n support for model names and attribute labels (besides other cool features > check it out!) .
But I want to factor in not only the plural form, but also the grammatical cases (especially the accusative) while translating 'Manage Objects', 'Create Object', 'Edit Object' etc.
When using themes you want to changes some of the translations specifically to the theme while keeping the standard translations for most of the text.
Duplicating the main translation file is a headache for maintainance.
This how to provides a solution.