Converting .gslides files to .txt format.
Converting Google Slides Shortcuts directly to Plain Text Files (.gslides to .txt conversion) is, per se, not possible, since the .gslides shortcuts do not contain any multimedia data. They merely link to an existing Google Slides object located on your Google Drive.
Simply open your presentation using the .gslides shortcut, then download it in a .txt format via the 'File -> Download As' function.
Client for a cloud storage and productivity service from Google
Presentation wep app from Google