According to doublage.qc.ca, the official canadian dubbing website:
This movie has been dubbed in Joual, a particular from of French Canadian language.
Here is an article I will try to translate the best I can:
Québec is facinated by the movie Slap Shot, released in 1977. ( . . . ) The translation in Canadian Quebec french was historical.
It was the first time an american movie was translated in our words, in québécois.
( . . . )
When Slap Shot was introduced in France, it was in a typically french version who did not convinced the writer Nancy Dowd. When Universal Pictures delegated the dubbig to Hubert Fielden, a French living in Quebec, he decided to do it in québécois without censoring anything. This ended with all the famous quotes that we all know by heart.
Here is an interview of Hubert Fielden where he says:
I told them it would be better in "québécois"! They asked me if I could adapt the dubbing and I said "Yes, I can!". It was the first time we dubbed a movie in "québécois" here.
( . . . )
Dubbers from Quebec were used to dub in international french, so at the beginning, it was more difficult.