You can't translate this directly, as it's an english 'casual' phrase.
some options could be, depending on the country we're using the spanish in,
'Vuelvo pronto' ([I will] come back soon) [polite]
'Ya vuelvo' ([I] come back) [casual]
'Volveré pronto' (I [am going to] come back soon) [polite]
These are pretty neutral, and unless you use specific dialect words, they should be understood by any spanish speaker