How to manage subtitles for dialects
I wouldn't do the second option at all. Subtitles should flow with the text, an comparision sign disturbs the flow.

I personally would prefere to simply rewrite the entire sentence.

Depending on your distribution media, I would make it closed captions, so people can turn off or on the translation.

Maybe, you could consider to translate the entire project, as this could be a less intrusive than switching subtitles on and off.

But I would handle it like most documentarys, when there are other languages involved. Simply translate the sentence.