Having a quick scan of your problem description on simplemathteam.wordpress.com, I would think that Perl is a really useful tool to solve the puzzle you pose. I would try, given a dictionary of English words:

• Based on string4, look for 6 letter words with the same letter in positions 3 and 4 and another one (or the same) in positions 1 and 5.
• See whether I find 7 letter words with the same letter in positions 3 and 4 for string3.
• Find words for strings 1 and 2 that fit to all possible choices for the above.

Perl is an excellent tool to do this!

What I find rather demotivating to offer you some more technical details is the fact that in simplemathteam.wordpress.com, you offer no link to the original encrypted text. So it is not clear what I would be helping you to achieve.

Update: Trying this strategy on 2of12inf from 12dicts does not find a solution for your problem. Issue is string2 which cannot be matched to any choices of string3 and string4. Interestingly, there are only 3 words to match string3. Hope this is helpful.

Update 2: Actually, re-reading your problem description, you are also looking at parts of English words, not complete words. Apologies for not reading in more detail. For that, one finds a lot of solutions.

Update 3: I do get ~1000 different combinations of 13 letters that can be covered with words from the dictionary. I am not taking into account cases where the end of one word and the beginning of another could cover the patterns.