zendframework/zendframework#6625 - s/de/del as per @Maks3w's review:

 > captcha es un nombre (no un adjetivo) por lo que `de` debería de ser `del` (de + el)
 >
 > captcha word is a noun (not an adjective) so you should replace `de` with `del`
 >
 > Lo mismo para las demás traducciones.
 >
 > Apply the same to the rest of translated messages.

languages/es/Zend_Captcha.php

@@ -12,12 +12,12 @@
  */
 return array(
     // Zend\Captcha\ReCaptcha
-    "Missing captcha fields" => "Faltan campos de captcha",
-    "Failed to validate captcha" => "La validación de captcha falló",
-    "Captcha value is wrong: %value%" => "El valor de captcha es erróneo: %value%",
+    "Missing captcha fields" => "Faltan campos del captcha",
+    "Failed to validate captcha" => "La validación del captcha falló",
+    "Captcha value is wrong: %value%" => "El valor del captcha es erróneo: %value%",
 
     // Zend\Captcha\Word
-    "Empty captcha value" => "Valor de captcha vacío",
-    "Captcha ID field is missing" => "Falta el campo ID de captcha",
-    "Captcha value is wrong" => "El valor de captcha es erróneo",
+    "Empty captcha value" => "Valor del captcha vacío",
+    "Captcha ID field is missing" => "Falta ell campo ID de captcha",
+    "Captcha value is wrong" => "El valor del captcha es erróneo",
 );