Jim mentions “Freedom Come All Ye” (Hamish Henderson), which is written in very broad Scots. Having lived in Scotland for nearly 40 years, and it being the song that is sung at most TMSA (Traditional Music & Song Association of Scotland) gatherings, I was determined to learn it: took me about 5 years only!
What helped was having a Scots-speaking singer go through it, word by word, explaining the meaning of each word. So I guess my point is, understanding what you’re singing about, whether you get the accent right or not, will make it more valid.