Complex sentence: The most common technique in multi-pass machine translation systems is to pre-process the input with a rule-based machine translation system, which passes its output to a statistical machine translation system, which produces the final output.
Split into simpler sentences: The most common technique in multi-pass machine translation systems is to pre-process the input with a rule-based machine translation system. The output of the rule-based pre-processor is passed to a statistical machine translation system, which produces the final output.