How hard is language reversal pair making within rule-based translation?

Language pair reversal: Rule-based translation is currently disregarded, in particular for the reason that it needs a lot of work and expertise. But is that reason well-grounded? Now focussing on a given language pair, we can formulate this question more accurately as follows: from a given pair language1/language2 translator, how much work is necessary to get a working translator language2/language1? To say it otherwise: aren’t there some techniques to speed up this process?