MINOR Removed i18nSSLegacyTranslator from default setup for performance reasons, document how to re-apply it

docs/en/changelogs/3.0.0.md

@@ -365,6 +365,34 @@ placeholder and the `PageComment` class. See the ['comments' module](https://git
 The setting determines difference homepages at arbitrary locations in the page tree,
 and was rarely used in practice - so we moved it to a "[homepagefordomain](https://github.com/silverstripe-labs/silverstripe-homepagefordomain)" module.
 	
+### Default translation source in YML instead of PHP $lang array, using Zend_Translate ###
+
+This allows for a more flexible handling of translation sources in various formats.
+Your own translations can be converted automatically via the ["i18n_yml_converter" module](https://github.com/chillu/i18n_yml_converter). Any modifications
+to the `$lang` global variable need to be re-applied via YML, or directly to the new translation adapters.
+
+	:::php
+	i18n::get_translator('core')->getAdapater()->addTranslation(array(
+		'content' => array('My.Entity' => 'My Translation'),
+		'locale' => 'en_US',
+		'usetranslateadapter' => true
+	));
+
+In order to keep backwards compatibility for PHP-based translations
+(from modules or your own code) without conversion, please add the following to your `_config.php`.
+Note that its just necessary if SilverStripe is used in a language other than the default (`en_US`).
+
+	:::php
+	i18n::register_translator(
+		new Zend_Translate(array(
+			'adapter' => 'i18nSSLegacyAdapter',
+			'locale' => i18n::default_locale(),
+			'disableNotices' => true,
+		)),
+		'legacy',
+		9 // priority lower than standard translator
+	);
+	
 ### Removed "auto-merging" of member records from `Member->onBeforeWrite()`
 
 Due to security reasons. Please use `DataObject->merge()` explicitly if this is desired behaviour.

i18n/i18n.php

@@ -1501,13 +1501,6 @@ class i18n extends Object implements TemplateGlobalProvider {
 					'disableNotices' => true,
 				))
 			);
-			self::$translators[$defaultPriority-1] = array(
-				'legacy' => new Zend_Translate(array(
-					'adapter' => 'i18nSSLegacyAdapter',
-					'locale' => self::$default_locale,
-					'disableNotices' => true,
-				))
-			);
 			
 			i18n::include_by_locale('en_US');
 		}