diff --git a/README.md b/README.md
index 8fc6152..f0bd545 100644
--- a/README.md
+++ b/README.md
@@ -59,6 +59,9 @@ See [documentation](https://kojix2.github.io/deepl.cr/).
   </tbody>
 </table>
 
+- When the environment variable `DEEPL_TARGET_LANG` is set, the method `DeepL::Translator#guess_target_language` will prioritize the language defined in `DEEPL_TARGET_LANG`. 
+- However, please note that this does not directly affect translation methods like `translate_text`.
+
 ## Development
 
 - Pull requests are welcome.