How to use openxml to get slide data by selection pane

Dear experts,

now i have a requirement to develop a translate powerpoint content.

I use OpenXML to extract the data from slide. But the result is all text in the slide.

is there any Class/API to get these text by its container which is in the powerpoint selection pane?

because i will write back the translated text to the same container.

Attach my current code, FYI:

public Dictionary<int,string> GetSlideIdAndText(string filePath, int index)
        {
            Dictionary<int, string> slideTexts = new Dictionary<int, string>();
            using (PresentationDocument ppt = PresentationDocument.Open(filePath, false))
            {
                // Get the relationship ID of the first slide.
                PresentationPart part = ppt.PresentationPart;
                OpenXmlElementList slideIds = part.Presentation.SlideIdList.ChildElements;

                string relId = (slideIds[index] as SlideId).RelationshipId;

                // Get the slide part from the relationship ID.
                SlidePart slide = (SlidePart)part.GetPartById(relId);

                // Get the inner text of the slide:
                IEnumerable<A.Text> texts = slide.Slide.Descendants<A.Text>();
                int i = 1;
                foreach (A.Text text in texts)
                {
                    slideTexts.Add(i,text.Text);
                    i++;
                }
            }
            return slideTexts;
        }
    }