diff --git a/locales/README.md b/locales/README.md
index 56bfae64d6..775a39a3c1 100644
--- a/locales/README.md
+++ b/locales/README.md
@@ -1,3 +1,6 @@
 # **DO NOT edit locale files** except `ja-JP.yml`.
 
+When you add text to the ja-JP file (of syuilo/misskey), it will automatically be applied to other language files.
+Translations added in ja-JP file should contain the original Japanese strings.
+
 Please see [Contribution guide](../CONTRIBUTING.md) for more information.