diff --git a/packages/angular/cli/lib/config/schema.json b/packages/angular/cli/lib/config/schema.json
index 38cab3f69297..66a59c26b58d 100644
--- a/packages/angular/cli/lib/config/schema.json
+++ b/packages/angular/cli/lib/config/schema.json
@@ -387,7 +387,8 @@
                   "type": "string",
                   "description": "Specifies the source locale of the application.",
                   "default": "en-US",
-                  "pattern": "^[a-z]{2}(-[a-zA-Z]{2,})?$"
+                  "$comment": "IETF BCP 47 language tag (simplified)",
+                  "pattern": "^[a-zA-Z]{2,3}(-[a-zA-Z]{4})?(-([a-zA-Z]{2}|[0-9]{3}))?(-[a-zA-Z]{5,8})?$"
                 },
                 {
                   "type": "object",
@@ -396,7 +397,7 @@
                     "code": {
                       "type": "string",
                       "description": "Specifies the locale code of the source locale",
-                      "pattern": "^[a-z]{2}(-[a-zA-Z]{2,})?$"
+                      "pattern": "^[a-zA-Z]{2,3}(-[a-zA-Z]{4})?(-([a-zA-Z]{2}|[0-9]{3}))?(-[a-zA-Z]{5,8})?$"
                     },
                     "baseHref": {
                       "type": "string",
diff --git a/packages/angular_devkit/core/src/experimental/workspace/workspace-schema.json b/packages/angular_devkit/core/src/experimental/workspace/workspace-schema.json
index c03dca716f93..a91285816f12 100644
--- a/packages/angular_devkit/core/src/experimental/workspace/workspace-schema.json
+++ b/packages/angular_devkit/core/src/experimental/workspace/workspace-schema.json
@@ -136,7 +136,7 @@
               "type": "string",
               "description": "Specifies the source locale of the application.",
               "default": "en-US",
-              "pattern": "^[a-z]{2}(-[a-zA-Z]{2,})?$"
+              "pattern": "^[a-zA-Z]{2,3}(-[a-zA-Z]{4})?(-([a-zA-Z]{2}|[0-9]{3}))?(-[a-zA-Z]{5,8})?$"
             },
             {
               "type": "object",
@@ -145,7 +145,7 @@
                 "code": {
                   "type": "string",
                   "description": "Specifies the locale code of the source locale",
-                  "pattern": "^[a-z]{2}(-[a-zA-Z]{2,})?$"
+                  "pattern": "^[a-zA-Z]{2,3}(-[a-zA-Z]{4})?(-([a-zA-Z]{2}|[0-9]{3}))?(-[a-zA-Z]{5,8})?$"
                 },
                 "baseHref": {
                   "type": "string",