Generally, the text of the pager could be changed dynamically via using the setOptions() method. However, this would cause the grid to reinitialize which would be unnecessary for changing only one span HTML element's content.
What I can recommend is to access the element with jQuery and alternate the text:
And this could be executed in the change event of the grid. With the help of the select() method, you would retrieve all of the selected rows.
Let me know in case additional assistance is required.
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