Step 1: the language

drag Igbo over to the right

save language choices

select Igbo

Step 2: Make word list

Start WordList tool, choose Igbo text and make sure it is in Unicode

Here is a shot of the frequency list. You can see the dots under O and I and U.

I don't know Igbo and therefore cannot be sure the word order is correct. At the moment WordSmith "thinks" this is Igbo so it is sorted in what Microsoft considers Igbo word order.