Vim: Reverse right to left

:set norl

or

:set norightleft

Each boolean option in Vim has a corresponding no-option that turns it off.

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The option you were originally looking for might have been relativenumber (rnu), which acts like number (nu) but adds line numbers that are relative to the current line rather than to the start of the editing buffer.

Turn options on or off with !

set rightleft!

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To quote the Vim help:

                                                           *:set-!* *:set-inv*
:se[t] {option}!   or
:se[t] inv{option}      Toggle option: Invert value. {not in Vi}

You can see this in the built-in Vim help by typing :help :set-! from inside Vim.