This is a developer variable that most users shouldn't have to worry about.

/opt chatcache
0 - Every character on the screen is drawn as a separate texture. (slow)
1 - When the chat is updated every character is drawn into a single texture. As long as no new text has a arrived. This texture is drawn on the screen. (very fast)
2 - When the chat is updated every character is blitted to an image then copied to a texture. (fast.. all cards).

When Toribash starts up it tries by default to set 1. If the graphics card can't handle that it sets 2.

Old versions use 0.