I live in Watford but all my father's side are Wiganers. I visited the town often as a child in the 70s and 80s to see my grandparents and other relatives. Family surnames include Walsh, Norburn and Urmston. They all originally lived around Lime Street (Flats), School Street and Lower Morris Street (old houses).
You can add this expression to your dictionary.
Wha's't'n't = Wha does tha not (Why does thou not)
I remember my great uncle Joe Norburn once said to me when I was about seven years old, "Wha's't'n't be a good lad?" (ie behave yourself)
The same expression was also used by another relative Ste Urmston to his dog, when it went for a swim in a the formerly polluted canal (or was it the River Douglas or the Yellow Brook).
"Coom airt o' t' watter! Wha's't'n't be a good dog?"
It must have been a very clever dog to understand such broad dialect.
Another word to add, Snig = Eel
I remember going fishing with my grandad (also Tom Walsh) at Bamber Bridge near Preston and reeling in numerous eels.
He used to say "Tha's cowt another bloody snig!"
It was the one type of fish he could never unhook with a disgorger or forceps. He always cut the line. Unlike other fish which were weighed and released, a "snig" needed an immediate execution which he performed by whipping the "snig" by its head on his fishing basket. For upto half an hour afterwards a dead "snig" with a mutilated head would continue trying to swim on the river bank.
The next sentence is merely broad Wigan accent rather than dialect words. It was said by my grandad's friend Bob Beach who lived in the same block in Limefield flats. The conversation was also about fishing.
"I cowt a few good peeuch in t' connel" ( I caught a few good perch in the canal )
Bob was renowned in Upper Morris Street WMC for boasting about catches but never giving a figure on anything. eg "It were a fair size. A good weight. I cowt a good many"
Two more expressions. I can't recall them being used in everyday conversations but they were told to me possibly by my grandad or my great uncle Jimmy Norburn.
Hie thee ! = hurry yourself up
Si thi = See thee (ie look) eg Si thi, t' mester's coomin (look, the boss/owner is coming)
Tekkin boggarts = taking fright and going mad , eg a cow trying to escape from the slaughterhouse
They've had tek 'im t' Billinge. = he's at death's door (So he's been sent to the hospital where nobody comes out alive)
Said about a number of elderly relatives before their sad demise.
th'Infirmary = the town's main general hospital
I've never known why you go to hospital down south but to th'Infirmary up north. This difference is not peculiar to Wigan , but is common to many northern towns.
"She'll not bart (bite) you. She's just gerrin (getting) a bit exsarted (excited), that's all" = my dog is actually a vicious wolf and you should stand clear.
Said by my second cousin Ste Urmston, who owned a bad tempered Alsatian, which later became too dangerous for him to keep and was either given away or put down.
I hope these are a useful addition to your dictionary. I doubt if many Wiganers under pension age use any of these expressions today. You may want to separate your words into modern and old Wigan dialect.