I have enabled 3 languages, but I always want to show Admin toolbar (menu) in English, I don't want that to be translated, how can I do that ? If I want to see front end content in Arabic then I don't want to see Admin menu in Arabic.
You can set a separate language for administrator pages on the account edit page for each administrator account.
Under Language settings, set the Administration pages language.
BUT! There is a major core bug related to this feature: if admins are creating fields, the config will be screwed up. See the issue for workarounds.
Admin toolbar module
If the question is specifically about the Admin Toolbar contrib module, you can not download the translation for it. If no translations are downloaded, the module will always show in English.
There's an issue on the Admin Toolbar module for this: https://www.drupal.org/project/admin_toolbar/issues/3004575