This happens when the Rocket League font file becomes corrupted. Follow these steps if Rocket League shows text as blocks █ █ █ :
- Go to C:\Program Files (x86)\Steam\steamapps\common\rocketleague\TAGame\CookedPCConsole
- Right click on GfxFonts.upk
- Select Delete
- How do I Verify the Integrity of Game Files on a PC?
If only some text shows up as blocks, but not all, the blocks may be unsupported characters. Unsupported characters are usually text in a different language, like Japanese or Arabic characters.