When attempting to enable Multilingual app toolkit on a project, nothing happens

For a .Net Standard project, edit the csproj file to add:

<PropertyGroup>
    <TargetFramework>netstandard2.0</TargetFramework>
    <NeutralLanguage>en-US</NeutralLanguage>
</PropertyGroup>

Add a line like this to your assemblyinfo.cs file:

[assembly: NeutralResourcesLanguage("en")] 

The indicated language is the one that the application currently uses (i.e usually hardcoded texts, before translation)