String Performance Question

My game contains large quantities of strings, every string will be used in my game and display it using one of the text UI. Right now, I write all my strings inside one of my C# scripts. Is it better to write them inside a txt file and read it each time I want the string to be displayed? How does this way influence the performance?

A text file would not be a more efficient way to store it, as you would have to implement a FileStream for reading and writing to the file, which has more overhead compared to the built in file type.