By default, subtitles are enabled in Lego Fortnite. To see how you can turn these off, you can take a look at this tutorial from Seeking Tech.
1. To start off, you need to head over to the Settings menu in the multiplayer game.
2. From there, you need to switch over to viewing the Audio tab.
3. Inside the Audio tab, select Sound on the left side.
4. You then need to select Subtitles on the right side of the same screen.
5. Once you get to the Subtitles menu, move the menu cursor down to the Subtitles setting and then make sure it is set to “Off.”
6. Apply the change and exit Settings.
When you start playing Lego Fortnite again, you should notice that there are no longer any subtitles.