In which XML file should I introduce translation

I’m confused about translations:
In spanish this msg is displayed:
##notification.sendNotificationConfirmation##
In english
Send notification email to all registered users

I order to add the Spanish translation I downloaded the en:US locale file but I cannot find either “notification.sendNotificationConfirmation” nor “Send notification email to all registered users” in any of the XML files.

Waht Im I doing wrong??? it should be somewhere???

Which version and which software you use?
If you use OJS please install Translator plugin and activate it and then go to Settings/Website/translation and manage that issue.

I use V 3.1.0.1
Translator pluggin is installed but I cannot locale in which file is the missing string

When You go to Translator plugin you will see on the left side small blue triangle and when you click on it you will see below option to translate. When you click on it you will see a list of various XML files. You will some in which is said that some strings are missing.
When you click on that file you will see emphasized strings and you can find your that is missing and translate it properly.

Thanks I understand how translator runs.
My question is (still) in which xml files are:
Spanish:
##notification.sendNotificationConfirmation##
English:
Send notification email to all registered users

I downloaded the en_US locale files but I cannot find either SO I DONT KNOW IN WHICH XML FILE I HAVE TO ADD THE TRANSLATION

Did you choose properly your locale?
Please check in locale/your locale/locale.xml

Did you choose properly your locale?
Locale is es_ES

Please go to translator plugin and check is that string in locale/es_ES/locale.xml

notification.sendNotificationConfirmation cannot be found in locale/es_ES/locale.xml, neither in the others XML files

Please check in forum whether this message key is one of missing message keys.

No information in forum about this ley

As far as I can see it should be ib /pkp/lib/locale/manager.xml

Do you see English message in interface for that message key?

OK i found it in /lib/pkp/locale/common.xml
i will edit it
Thanks