Here is my code for localizing the Sum aggregate function. The obtained result is a partial translation:

        public RadForm1()
        {
            PivotGridLocalizationProvider.CurrentProvider = new MyEnglishPivotGridLoclizationProvider();
            InitializeComponent();
        }

        private void RadForm1_Load(object sender, EventArgs e)
        {
            this.ordersTableAdapter.Fill(this.nwindDataSet.Orders);

            this.radPivotGrid1.RowGroupDescriptions.Add(new DateTimeGroupDescription() { PropertyName = "OrderDate", Step = DateTimeStep.Year, GroupComparer = new GroupNameComparer() });
            this.radPivotGrid1.RowGroupDescriptions.Add(new DateTimeGroupDescription() { PropertyName = "OrderDate", Step = DateTimeStep.Quarter, GroupComparer = new GroupNameComparer() });
            this.radPivotGrid1.RowGroupDescriptions.Add(new DateTimeGroupDescription() { PropertyName = "OrderDate", Step = DateTimeStep.Month, GroupComparer = new GroupNameComparer() });
            this.radPivotGrid1.ColumnGroupDescriptions.Add(new PropertyGroupDescription() { PropertyName = "EmployeeID", GroupComparer = new GrandTotalComparer() });
            this.radPivotGrid1.AggregateDescriptions.Add(new PropertyAggregateDescription() { PropertyName = "Freight", AggregateFunction = AggregateFunctions.Sum });
            this.radPivotGrid1.AggregateDescriptions.Add(new PropertyAggregateDescription() { PropertyName = "Freight", AggregateFunction = AggregateFunctions.Count });
            this.radPivotGrid1.FilterDescriptions.Add(new PropertyFilterDescription() { PropertyName = "ShipCountry", CustomName = "Country" });
            this.radPivotGrid1.DataSource = this.ordersBindingSource;
        }

        class MyEnglishPivotGridLoclizationProvider : PivotGridLocalizationProvider
        {
            public override string GetLocalizedString(string id)
            {
                switch (id)
                {
                    case PivotStringId.Sum:
                        return "Soma"; 
                    default:
                        return base.GetLocalizedString(id);
                }
            }
        }

The "Sort" item doesn't seem to be relevant for the report filter. It should be removed from the menu items. However, for the "Hide" item it can be added logic for removing the filter:

GroupDescriptions loose the Custom Name after dragging.

The error is reproducible in the First look example of RadPivotGrid:

Hello,

I am using the pivot grid control would like to know if it is possible to add a start and end to the grouping?

My pivot grid looks like this: I would like the user to be able to specify a start and end for the grouping.

Excel has this option:

How can I replicate this functionality?

As a user I want to hide the Grand Totals for specific groups:

The group description now has AutoShowSubTotals property determining whether subtotals will be generated for the description:

this.radPivotGrid1.RowGroupDescriptions.Add(new DateTimeGroupDescription
{
    PropertyName = "OrderDate",
    Step = DateTimeStep.Quarter,
    GroupComparer = new GroupNameComparer(),
    AutoShowSubTotals = false
});

Check the attached screenshot:

Hour, minute, second, if possible also week

Workaround:

Use the new PivotGridSpreadExport

To reproduce: 

- Set the ExportFlatData property to true

- Export the grid using PivotExportToExcelML

How to reproduce: see the attached video

Workaround:
public partial class Form2 : Form
{
    public Form2()
    {
        InitializeComponent();

        this.radPivotFieldList1.DragDropService = new CustomPivotFieldListDragDropService(this.radPivotFieldList1);
    }

    private void Form2_Load(object sender, EventArgs e)
    {
        // TODO: This line of code loads data into the 'nwindDataSet.Orders' table. You can move, or remove it, as needed.
        this.ordersTableAdapter.Fill(this.nwindDataSet.Orders);

    }
}

public class CustomPivotFieldListDragDropService : PivotFieldListDragDropService
{
    private RadPivotFieldList fieldList;
    private Telerik.WinControls.UI.PivotFieldList.FieldPayload payload;

    public CustomPivotFieldListDragDropService(RadPivotFieldList fieldList)
        : base(fieldList)
    {
        this.fieldList = fieldList;
    }

    protected override void PerformStart()
    {
        base.PerformStart();

        Telerik.WinControls.UI.PivotFieldList.IField draggedField = this.GetField(this.Context);

        if (draggedField == null)
        {
            this.Stop(false);
            return;
        }

        this.payload = new Telerik.WinControls.UI.PivotFieldList.FieldPayload(draggedField);
    }

    protected override void OnPreviewDragOver(RadDragOverEventArgs e)
    {
        RadElement targetElement = this.DropTarget as RadElement;
        Telerik.WinControls.UI.PivotFieldList.IField targetField = this.GetField(targetElement);

        if (targetElement != null && targetElement.ElementTree.Control == this.fieldList.ReportFiltersControl && this.payload != null)
        {
            foreach (Telerik.WinControls.UI.PivotFieldList.IField field in this.fieldList.ViewModel.Filters)
            {
                if (field.FieldInfo == payload.DraggedField.FieldInfo &&  this.Context is TreeNodeElement ))
                {
                    e.CanDrop = false;
                    this.payload.SetDestination(null);
                    this.payload.RemoveFromSource = false;

                    return;
                }
            }
        }

        base.OnPreviewDragOver(e);
    }

    private Telerik.WinControls.UI.PivotFieldList.IField GetField(object context)
    {
        RadListVisualItem listItem = context as RadListVisualItem;
        TreeNodeElement treeItem = context as TreeNodeElement;
        PivotFieldListItemButton button = context as PivotFieldListItemButton;

        if (button != null)
        {
            listItem = button.Owner;
        }

        Telerik.WinControls.UI.PivotFieldList.IField field1 = null, field2 = null;
        if (listItem != null && listItem.Data != null)
        {
            field1 = listItem.Data.DataBoundItem as Telerik.WinControls.UI.PivotFieldList.IField;
        }

        if (treeItem != null && treeItem.Data != null)
        {
            field2 = treeItem.Data.DataBoundItem as Telerik.WinControls.UI.PivotFieldList.IField;
        }

        return field1 ?? field2;
    }
}

Workaround: If possible add the label filters with code
PropertyGroupDescription dateGroupDescription = new PropertyGroupDescription();
dateGroupDescription.PropertyName = "Date";

LabelGroupFilter filter = new LabelGroupFilter();
ComparisonCondition condition = new ComparisonCondition
{
    Condition = Telerik.Pivot.Core.Filtering.Comparison.IsGreaterThan,
    Than = new DateTime(2010, 6, 6)
};
filter.Condition = condition;
dateGroupDescription.GroupFilter = filter;

this.provider.RowGroupDescriptions.Add(dateGroupDescription);

The issue may manifest if aggregate descriptions are added on the pivot`s column axis and if their member does not return data.