After Spike sacrificed himself to save the world, Buffy was crushed. She spent years appealing to the PTB to bring Spike back from Hell. They finally relent and agree to bring him back to Earth. But Whistler, annoyed by her incessant nagging about it, decides to send Spike’s soul back to a less convenient time for her. He chooses to implant Spike’s soul into his body a full year before his sacrifice ever took place—moments after Buffy leaves him in a huff in the abandoned house they brought down together the night before in “Smashed.”

When Spike wakes up from the jarring ordeal, he remembers only having been in Hell for thousands of years (in Hell-time). He can’t even initially remember English, speaking a language only spoken in Hell. Only Anya can translate for him until his memory returns, ex-vengeance demon that she is. Buffy decides to take care of Spike and help him readjust to life on Earth and through him sees a new perspective on her own troubles with the prospect. Eventually, the Scoobies get an explanation from Whistler. 

Up to you:

If you want to flesh out what a Hell language might be like. (I had had ideas that it would be suffering-based with no words for pleasure or positive things, and no quantifying words as that would imply finality.) You could have maybe have fun with it…