Jeffrey and ratbak, thanks for your pointers.
Sorry for this late response. The question came up because of a wish and not a hard requirement. And something came up with a high priority, so I had to work on that. But I should have thanked you for your time and attention, but this didn't have my attention at that moment. I should have been more polite and considerate toward you (sorry).
Both answers could be the start of a solution. (Maybe substiting some words which are equivalent or similar). And then using the algoritm. And then finding the texts with the 'shortest' Levenshtein Distance. Or finding groups where the Levenshtein Distance is shortest between the texts.
For your information the texts are recipe's for preparing medication, so equivalence is (big question mark) is more based on understanding the recipe than on actual equivalence in writing.
Both techniques are new to me, so I'll first have a further look into the your links. And see if I can come up with an implementation, without spending to much time on this. (As said it is not a requirement, but would be a nice to have). And then see if this produces a workable situation.