en_tn/gen/18/20.md

the cries about Sodom and Gomorrah

This could be translated as "the outcry against Sodom and Gomorrah." People were crying out because the people of Sodom and Gomorrha were so wicked. They may have been crying out to God to punish them.

their sin is so very grave

"their sin is so serious" or "they have sinned so much"

I will now go down there

"I will now go down to Sodom and Gomorrah"

go down there and see

"go down there to find out" or "go down there to decide"

as wicked as the outcry which has come to me suggests

This can also be translated as "as wicked as I have heard they are."

If not

"If they are not as wicked as the outcry suggests"