Improved description of how Yii handles plural rules

docs/guide/tutorial-i18n.md

@@ -257,9 +257,10 @@ for Russian:
 
 In the above it's worth mentioning that `=1` matches exactly `n = 1` while `one` matches `21` or `101`.
 
-Note, that you can not use the Russian example in `Yii::t()` directly, you have to adjust the
-[[yii\base\Application::$sourceLanguage|source language]] setting in your application config
-so that Yii knows which language you are using to apply the correct plural rules.
+Note, that you can not use the Russian example in `Yii::t()` directly if your
+[[yii\base\Application::$sourceLanguage|source language]] isn't set to `ru_RU` which is not recommended. Instead, such
+strings should end up in message files or message database (in case DB source is used). Yii uses plural rules of the
+language strings are translated to and is falling back to plural rules of source language if translation isn't available.
 
 To learn which inflection forms you should specify for your language you can referrer to the
 [rules reference at unicode.org](http://unicode.org/repos/cldr-tmp/trunk/diff/supplemental/language_plural_rules.html).