If you trust that all misspellings are relatively uncommon, you can start by approving common words (with a threshold you set, e.g. 100+, or 25+, or 10+ occurrences). In PT9 this is in the Tools menu of the spelling list.
Also, I found that one good way to catch misspellings is to use the Find Similar Words feature. In the dialog you can specify what are sources of misspellings in your language (these are specified in the box “letters that sound alike”, e.g. p/pp, b/bw, k/g, a/aa, ee/ei, e/é…, and the box “Letters to ignore”, e.g. y, w – whatever letters and/or diacritics tend to be confused in the language under consideration). Obviously, the longer the list of similar pairs is, the more matches will show up in the list of similar words, and some of these may be valid spellings of different words. But still, the feature can be very helpful. For example, it will show word pairs that are spelled almost identically, but with a difference at the start of the word - these pairs won’t be close to each other in the overall list.
Paulus+Kieviet