As mentioned above, add a subtitle with smaller font above or below the main title.
This feature is mostly for modpacks, so it should be blank in default.
also this mod should add some debug commands for developers. here are some commands I think it should have:

• list the available biomes with their titles
• show a specified titles (even when not in the correct biome)
• a test command to quickly check the effects of the title

Some great ideas here. Although I'm not sure how practical it is to list all biomes and their titles. Can you elaborate on what you mean by checking the effects of the title?

Added /biometitle and /dimensiontitle in v1.3.

firstly thanks for using some of my ideas!

secondly, the reason of why I will ask for biomes list is for this.
Is probably a subbiome from Autumnity ,which use to spawn some maple tree in dark forest.
I know I can use biome group, but I don't know where to get it's "codename", I'm not very good at this area.

And by the way, did you intend to add subtitles?

ohh, surry for being ignorance! I didn't notice's that I can actually find it in any command relate to biomes!