fix: Change translation domain name for bundle translation and add an example

Author: jbonnier

bundles/best_practices.rst

@@ -397,10 +397,14 @@ Translation Files
 -----------------
 
 If a bundle provides message translations, they must be defined in the XLIFF
-format; the domain should be named after the bundle name (``acme_blog``).
+format; the domain should be named after the bundle name (``AcmeBlog``).
 
 A bundle must not override existing messages from another bundle.
 
+The translation domain should match the translation file names. For example,
+if the translation domain is ``AcmeBlog``, the English translation file name
+should be ``AcmeBlog.en.xlf``.
+
 Configuration
 -------------