Basically, unlike what the docs say, manually setting a SourcePath is mandatory if you want a local/offline install, and the source path should exclude the top level directory name of the install bundle (so should not end with Office unless you've got a folder named Office inside another folder named Office).

Step 2: Configure Microsoft 365 language. After you install the language accessory pack, you must configure Microsoft 365 for your new language preferences. This configuration affects all your Microsoft 365 applications. Note: If you're using Office 365 and the commands available are different from what's shown here, click the Office 2016 tab

To install the Visual Studio Tools for Office runtime. Install the .NET Framework 4 or later. To download the .NET Framework 4, see Microsoft .NET Framework 4 (Web Installer). To download the .NET Framework 4 Client Profile, see Microsoft .NET Framework 4 Client Profile (Web Installer).

The DISM.exe /Add-Package command allows you to install an MSU update as well (only the offline Windows image is supported). You can use the /PackagePath parameter to specify a path to the directory where the MSU and CAB update files are stored.
From that Office link, above: "If your Office 2016 or Office 2013 product is included under one of the Office for home plans and you're having problems with slow speed or unreliable connections, you can download the offline installer file.
Step 1 - Download the Visual Studio bootstrapper. Download the correct bootstrapper for the version and edition of Visual Studio you want and copy it into the directory that you want to serve as the source location of your local layout. The bootstrapper is the executable that you use to create, update, or modify your local layout. You must have . 298 140 215 392 255 303 21 350 316

how do i download office 2019 offline installer