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You won't be able to do that because of a WordPress restriction. All multisite installations MUST be installed in the root of the domain name. That means that you can only restore your multisite installation into http://localhost but NOT a subdirectory such as http://localhost/wptest.

Unfortunately this is not something that has to do with Akeeba Backup. Akeeba Backup can and does replace all the internal URLs with the new ones. The problem lies in WordPress itself and the black magic it does under the scenes to give you the illusion of a multisite installation. It has a hardcoded assumption that the first segment of the URL path (the thing after the first forward slash and before the second forward slash, if it exists) is the multisite name. That's why it's not possible to restore to a straight up XAMPP environment.

Can you restore mutlisites locally? Absolutely, but it needs trickery on your part. It requires creating custom DNS records for a live domain and a virtual host on your Apache installation. It's complicated (to put it mildly). Alternatively you can use MAMP Pro for Windows or for Mac (unfortuantely a paid solution) to create a local, fake domain such as http://wptest.damiaan - but this won't work with Microsoft Edge for obscure technical reasons.

Note that none of these would be necessary if WordPress did a better job at handling multisite installations. Unfortunately that's not the case. I am as frustrated as you are for two reasons. First, this makes it hard for me to assess multisite WordPress transfers for development and pre-release testing. Second, you are by far not the first person to ask that question. We get it at least once a week, half of the times reported as a bug. The perils of being the only backup solution to support multisite restoration to a different server, I guess.

I believe that has to do with the way WordPress sets up the .htaccess file. However, I have not been able to find the conditions which allow a multisite to work successfully inside a subdirectory.