Modify InstalledUICulture in c#

Question

Is there a way to change InstalledUICulture from English to Germany in test?

var groups = new ObservableDictionary<string, IGroupViewModel>(vm => 
    vm.Name.ToString(CultureInfo.InstalledUICulture));
var isGroupExists = groups.ContainsKey(GroupName.ToString(CultureInfo.InstalledUICulture));
if (!isGroupExists)
{
     groups.Add(new GroupViewModel());
}

Answer 1

Can you please give me some example?

Something like this. Instead of coupling your code directly to CultureInfo.InstalledUICulture you use a layer of indirection to allow you to pretend that the current UI culture is whatever you want.

I don't know your classes or how you are creating services, but I've assumed some sort of DI and used constructor parameters for the provider (or service or whatever you want to call it)

// App code
public interface ICurrentCultureProvider {
    CultureInfo CurrentInstalledUICulture { get; }
}

public class CurrentCultureProvider : ICurrentCultureProvider {
    public CultureInfo CurrentInstalledUICulture => CultureInfo.InstalledUICulture;
}

public class SUT {
    private readonly ICurrentCultureProvider cultureProvider;

    public SUT(ICurrentCultureProvider cultureProvider) {
        this.cultureProvider = cultureProvider;
    }

    public object Method(??? vm) {
        var currentUICulture = cultureProvider.CurrentInstalledUICulture;
        var groups = new ObservableDictionary<string, IGroupViewModel>(vm => vm.Name.ToString(currentUICulture));
        var isGroupExists = groups.ContainsKey(GroupName.ToString(currentUICulture));

        if (!isGroupExists) {
            groups.Add(new GroupViewModel());
        }

        return groups;
    }
}

// Test code. Could make this return any culture by using a parameter.
public class GermanCultureProvider : ICurrentCultureProvider {
    public CultureInfo CurrentInstalledUICulture => new CultureInfo("de-DE");
}

[TestFixture]
public class Sample_Test {

    [Test]
    public void Demo() {
        var sut = new SUT(new GermanCultureProvider());
        var vm = new ???();
        var groups = sut.Method(vm);
        // Assert correct in German etc
    }
}