Linguistics. My thesis looked at how people who speak more than one language will sometimes use words from one language in order to get at specific nuances and shades of meaning that don't translate well. I took 25 hours of video and audio recordings of people from Alberta, Canada and from Maine in the US talking in French and English, found the most common English words that they used out of all of that, and looked at how and when they were using them to see if they had any special meanings or uses for them!
I'm wondering if Strine might be a useful inclusion on your PhD course; unfortunately Afferbeck Lauder's book is now out of print. Oops - I tell a lie! A search found Let Stalk Strine / Nose Tone Unturned
Not really your field but you may find it fun if you ever come across it. It is based on the Australian tendency to drop most vowels as useless impediments to speech and shorten words whenever possible. A few examples which will only make sense if spoken aloud:
MNX: breakfast, low carb.
Egg Nishner: device to keep a room cool.
Cancel: mob of crooks who force house owners to pay rates.
Emma Chisit: request for the price