[Form] add missing Czech validators translation

Author: mhujer

Resources/translations/validators.cs.xlf

@@ -14,6 +14,10 @@
                 <source>The CSRF token is invalid. Please try to resubmit the form.</source>
                 <target>CSRF token je neplatný. Zkuste prosím znovu odeslat formulář.</target>
             </trans-unit>
+            <trans-unit id="99">
+                <source>This value is not a valid HTML5 color.</source>
+                <target>Tato hodnota není platná HTML5 barva.</target>
+            </trans-unit>
         </body>
     </file>
 </xliff>