[Database] Add 'creation_datetime' to User + some little things

backend/src/main.rs

@@ -245,7 +245,11 @@ async fn translation(
                     .map(|l| l.split('-').next().unwrap_or_default())
                     .find_or_first(|l| available_codes.contains(l));
 
-                accept_language.unwrap_or("en").to_string()
+                match accept_language {
+                    Some(lang) if !lang.is_empty() => lang,
+                    _ => translation::DEFAULT_LANGUAGE_CODE,
+                }
+                .to_string()
             }
         }
     };