Merge branch 'winh-sprintf-no-escape-docs' into 'master'

Document example for sprintf without escaping

See merge request gitlab-org/gitlab-ce!16712

doc/development/i18n/externalization.md

@@ -131,6 +131,9 @@ There is also and alternative method to [translate messages from validation erro
 ### Interpolation
+Placeholders in translated text should match the code style of the respective source file.
+For example use `%{created_at}` in Ruby but `%{createdAt}` in JavaScript.
+
 - In Ruby/HAML:
     ```ruby
@@ -141,11 +144,19 @@ There is also and alternative method to [translate messages from validation erro
     ```js
     import { __, sprintf } from '~/locale';
-    sprintf(__('Hello %{username}'), { username: 'Joe' }) => 'Hello Joe'
+
+    sprintf(__('Hello %{username}'), { username: 'Joe' }); // => 'Hello Joe'
     ```
-The placeholders should match the code style of the respective source file.
-For example use `%{created_at}` in Ruby but `%{createdAt}` in JavaScript.
+    By default, `sprintf` escapes the placeholder values.
+    If you want to take care of that yourself, you can pass `false` as third argument.
+
+    ```js
+    import { __, sprintf } from '~/locale';
+
+    sprintf(__('This is %{value}'), { value: '<strong>bold</strong>' }); // => 'This is &lt;strong&gt;bold&lt;/strong&gt;'
+    sprintf(__('This is %{value}'), { value: '<strong>bold</strong>' }, false); // => 'This is <strong>bold</strong>'
+    ```
 ### Plurals