Given a large number of entries in the source of data validation, it may become cumbersome to scroll down the list to select a desired value. It would be ideal to have the user type the first alphabet and be taken to all words which start with that alphabet.
The drop down list in cell C2 is the normal drop down list created through data validation. This list does not have your desired functionality. However, the drop down list in cell E2 has the desired functionality. In cell E2, type the first letter of the any alphabet and then click the drop down button in the cell. You will be taken to the first alphabet int he list.
You may refer to my solution in this workbook.