Add a doc explaining how to force output to a specific locale

Author: danielbachhuber

bin/handbook-manifest.json

@@ -53,6 +53,12 @@
         "markdown_source": "https:\/\/github.com\/wp-cli\/handbook\/blob\/master\/external-resources.md",
         "parent": null
     },
+    "force-output-specific-locale": {
+        "title": "Force output to a specific locale",
+        "slug": "force-output-specific-locale",
+        "markdown_source": "https:\/\/github.com\/wp-cli\/handbook\/blob\/master\/force-output-specific-locale.md",
+        "parent": null
+    },
     "governance": {
         "title": "Governance",
         "slug": "governance",

force-output-specific-locale.md

@@ -0,0 +1,36 @@
+# Force output to a specific locale
+
+WP-CLI always outputs English because it doesn't support localization. But, because WordPress supports localization, you may see non-English output when performing specific commands.
+
+For instance:
+
+    $ wp theme update --all
+    מעבר למצב תחזוקה...
+    מוריד עדכונים מ-https://downloads.wordpress.org/theme/hueman.3.3.25.zip...
+    Using cached file '/home/xxx/.wp-cli/cache/theme/hueman-3.3.25.zip'...
+    פתיחת עדכון...
+    התקנת גרסה חדשה...
+    הסרת הגרסה הקודמת של התבנית...
+    התבנית עודכנה בהצלחה.
+    ביטול מצב תחזוקה...
+    +--------+-------------+-------------+---------+
+    | name   | old_version | new_version | status  |
+    +--------+-------------+-------------+---------+
+    | hueman | 3.3.24      | 3.3.25      | Updated |
+    +--------+-------------+-------------+---------+
+    Success: Updated 1 of 1 themes.
+
+To force WordPress to always output English at the command line, you need to filter the active locale.
+
+Given a `force-locale.php` file:
+
+    <?php
+    WP_CLI::add_wp_hook( 'pre_option_WPLANG', function() {
+	    return 'en_US';
+    });
+
+You can force the locale to `en_US` with:
+
+    wp --require=force-locale.php
+
+One nice thing about this approach is that you can easily apply it across multiple WP installs [using a config file](https://make.wordpress.org/cli/handbook/config/#config-files).