the text for the notifications are not stored in the language manager at "edit language". To translate the notifications you have to go to the settings at https://myshopify.com/admin/settings/notifications and change the text directly in the notification templates.
Since the templates written in HTML and Liquid please be careful. If you're not familiar with HTML and Liquid I recommend using an app like OrderlyEmails https://is.gd/z9CxHS
As far as I know they don't support arabic yet, but within the app it's much easier to make the translation for the notifications.
I can also offer our translating app Langshop to you. We support Arabic as well as over 240 different languages. You can add up to 5 additional languages except your default one if you have a Basic Shopify plan.
The only specific is that the app does not handle your default language content. So, you can translate your default language content to any language, but first, you have to establish everything within your default store language version. Anyway, we have a lot of different advantages and powerful possibilities to make your business really multilingual and multi-currency.
Ask us everything you want to know about our app at any time: firstname.lastname@example.org