Getting a list of similar spelling words

Question

Programming

Given a text variable (4 characters, only numbers and Russian letters).
You need to somehow get a list of similar words from what is given. (list of combinations)
Well, respectively, in the example:
A English is similar to A Russian,
P English to Russian P,
O English is similar to Russian O. and also zero.
In a specific example, the word ААР is given, the result of processing should be a list of the form: (small letters - the English alphabet).
AAP
AAp
AaP
Aap
aAP
aAp
aaP
aap
It doesn't matter what language, words or block diagram. The main principle is to understand. Although I would be grateful for specific examples.

Answer 1

the third link from the top in google explains with an example.
the fourth is for an online service.
the sixth - to a macro in msword.
google.com ;)