gst-convert can be used. It also supports rewrite rules to fix dialect incompatibilities automatically. You can write a script called, for example, gst-squeak like this one:

#! /bin/sh
#
# usage: gst-squeak SOURCE DEST
#
# Converts Squeak code to GNU Smalltalk
# Stymied by code like "foo-10" (notice no space around the
# minus), otherwise should work fine.

exec gst-convert -f squeak \ 
  -r'MessageSend->DirectedMessage' \ 
  -r'DateAndTime->DateTime' \ 
  -r'(``@object ifNil: ``@arg ifNotNil: [ | `@t2 | `@.s2 ] )-> 
     (``@object ifNil: ``@arg ifNotNil: [ :foo || `@t2 | `@.s2 ])' \ 
  -r'(``@object ifNotNil: [ | `@t2 | `@.s2 ] ifNil: ``@arg )->
     (``@object ifNotNil: [ :foo || `@t2 | `@.s2 ] ifNil: ``@arg)' \ 
  -r'(``@object ifNotNil: [ | `@t2 | `@.s2 ] )->
     (``@object ifNotNil: [ :foo || `@t2 | `@.s2 ])' \ 
  -r'(``@object ifNil: ``@arg1 ifNotNilDo: ``@arg2 )->
     (``@object ifNil: ``@arg1 ifNotNil: ``@arg2)' \ 
  -r'(``@object ifNotNilDo: ``@arg2 ifNil: ``@arg1 )->
     (``@object ifNotNil: ``@arg2 ifNil: ``@arg1)' \ 
  -r'(``@object ifNotNilDo: ``@arg2 )->
     (``@object ifNotNil: ``@arg2)' \ 
  -r'(``@object doIfNotNil: ``@arg2 )->
     (``@object ifNotNil: ``@arg2)' \ 
  -r'(``@object newFrom: ``@arg2 )->
     (``@object from: ``@arg2)' \ 
  -r'(Dictionary withAll: ``@arg2 )->
     (Dictionary from: ``@arg2)' \ 
 "$@"