diff --git a/backend/sql/version_1.sql b/backend/sql/version_1.sql
index 0e44445..446d79e 100644
--- a/backend/sql/version_1.sql
+++ b/backend/sql/version_1.sql
@@ -69,7 +69,7 @@ CREATE TABLE [Recipe] (
     [id] INTEGER PRIMARY KEY,
     [user_id] INTEGER, -- Can be null if a user is deleted.
     [title] TEXT NOT NULL,
-     -- https://en.wikipedia.org/wiki/List_of_ISO_639_language_codes
+     -- https://en.wikipedia.org/wiki/List_of_ISO_639_language_codes (Set 1).
     [lang] TEXT NOT NULL DEFAULT 'en',
     [estimated_time] INTEGER, -- in [s].
     [description] TEXT NOT NULL DEFAULT '',
@@ -80,6 +80,7 @@ CREATE TABLE [Recipe] (
     [creation_datetime] TEXT NOT NULL,
 
     CHECK (
+        length([lang]) = 2 AND
         length([title]) <= 255 AND
         length([description]) <= 65535 AND
         [difficulty] >= 0 AND [difficulty] <= 3