Basically, go to C:\Program Files (x86)\Steam\steamapps\common\Risk of Rain 2\Risk of Rain 2_Data\Language\en in which then you will find a few .txt files in which you can freely edit with.
I recommend only editing characterbodies.txt, which are the character names, description, abilities and ability names. For item and description.txt, i advise changing the description of items and equipments into more detailed versions.

You can find a guide on how to get detailed item and equipment descriptions in the guides section.
Feel free to explore around and see what you can edit or change, however, i do not rlly know what would happen if you were to delete these .txt files, if you dont know what the .txt files do, do not edit or change anything then.
Personally, i have only changed the character names and item names, i also changed my item and equipment into a more detailed explaination. I AM NOT RESPONSIBLE IF YOU ♥♥♥♥ UP AND DELETE CERTAIN FILES THAT MAKE THE GAME BROKEN.
That concludes the end of this guide and i wish you luck in editing .txt files


Note: if like all of you guys already know how to edit the .txt files then i am pretty retarded.

If we go to the characterbodies.txt file, and go to REX's section, we can see something called "TREEBOT_BODY_LORE", and after that is text that relates to REX's lore. Now, in order to get the other characters to have lore, you just copy paste the "TREEBOT_BODY_LORE" line and paste it below any character you want, Rename "TREEBOT_BODY_LORE" to something like "COMMANDO_BODY_LORE" for example, if you wish to change the lore of commando.
For the format to input the lore, you can copy paste from rex's: and just edit it to whatever you want. However, remember to use " " inbetween ur text and after that, always add a comma if not the other text for other characters wont be recognized by the game. P.s you can copy my format:
Replace the words in brackets and remember to remove the brackets too, also dont forget the comma at the end.
"(enter name of character here)_BODY_LORE" : "<style=cSub>\r\n\r\n(Enter text here)\r\n<\/style>\r\n",