Multi Substitution -- No VBA

What is the best method for searching and replacing within a string when the string to be replaced could be say 1 of 10 options and could appear in any position within the string ? To make it easier let's say wherever those sub strings appear they are to be replaced (ie none to be left behind), and lets say they are all to be replaced by another character -- specific to each string being replaced.

Example:

Say I want to replace any digits in a string, to be replaced like for like as follows:

0 -> a
1 -> b
2 -> c
3 -> d
4 -> e
5 -> f
6 -> g
7 -> h
8 -> i
9 -> j

Sample strings:

Luke is 0 Donkey
Luke is 0 Mul4
0nd Luk4 is not very cl4v4r
Luke can not h40r very w4ll.

etc...