Add new error message for invalid dkim slector #6459

As the regex condition changed, the error message for invalid did too.
Lanuage files for en/de/es are now state the new rules for a valid selector.

Author: Demian

interface/web/mail/lib/lang/de_mail_domain.lng

@@ -17,7 +17,7 @@ $wb['limit_maildomain_txt'] = 'Die maximale Anzahl an E-Mail Domains für Ihr Ko
 $wb['policy_txt'] = 'Spamfilter';
 $wb['no_policy'] = '- nicht aktiviert -';
 $wb['dkim_selector_txt'] = 'DKIM-Selector';
-$wb['dkim_selector_error'] = 'Ungültiger DKIM-Selector.  Verwenden Sie nur max. 63 alphanumerische Zeichen (a-z oder 0-9)';
+$wb['dkim_selector_error'] = 'Ungültiger DKIM-Selector. Verwenden Sie nur max. 63 alphanumerische Zeichen (a-z oder 0-9), gefolgt von einem optionalen Punkt und weiter 63 alphanumerischen Zeichen.';
 $wb['dkim_settings_txt'] = 'DomainKeys Identified Mail (DKIM)';
 $wb['error_not_allowed_server_id'] = 'Chosen server is not allowed for this account.';
 $wb['relayhost_txt'] = 'Relayhost';

interface/web/mail/lib/lang/en_mail_domain.lng

@@ -19,7 +19,7 @@ $wb['policy_txt'] = 'Spamfilter';
 $wb['no_policy'] = '- not enabled -';
 $wb['error_not_allowed_server_id'] = 'Chosen server is not allowed for this account.';
 $wb['dkim_selector_txt'] = 'DKIM-Selector';
-$wb['dkim_selector_error'] = 'Invalid DKIM-Selector. Use only lower-case alphanumeric characters (a-z or 0-9) up to 63 chars';
+$wb['dkim_selector_error'] = 'Invalid DKIM-Selector. Use only lower-case alphanumeric characters (a-z or 0-9) up to 63 chars, optional followed by a period and by another string of no more than 63 lower-case alphanumeric characters.';
 $wb['relayhost_txt'] = 'Relayhost';
 $wb['relayhost_user_txt'] = 'Relayhost User';
 $wb['relayhost_password_txt'] = 'Relayhost Password';

interface/web/mail/lib/lang/es_mail_domain.lng

@@ -6,7 +6,7 @@ $wb['dkim_generate_txt'] = 'Generar clave privada DKIM';
 $wb['dkim_private_key_error'] = 'Clave privada DKIM no válida';
 $wb['dkim_private_txt'] = 'Clave privada DKIM';
 $wb['dkim_public_txt'] = 'Clave pública DKIM\nsólo para información';
-$wb['dkim_selector_error'] = 'Selector DKIM no válido. Use como máximo 63 caracteres alfanuméricos en minúsculas (a-z o 0-9)';
+$wb['dkim_selector_error'] = 'Selector DKIM inválido. Utilice <subdominio(.subdominio)>. El subdominio tiene un máximo de 63 caracteres en minúsculas <a-z y 0-9> y el segundo subdominio es opcional';
 $wb['dkim_selector_txt'] = 'Selector DKIM';
 $wb['dkim_settings_txt'] = 'Correo Identificado por Claves de Dominio (DKIM)';
 $wb['dkim_txt'] = 'Activar DKIM';