Pembwe and the Southeast is the hot humid region of Tanzania including the principal city Dar es Salaam and most of the country's Indian Ocean coastline.
As with the rest of Tanzania, Swahili is the main language spoken, however you may come across tribal dialects such as Makonde or a mish mash of the two. English is spoken sporadically, tourists are rare in these parts so there has not been an incentive for people to learn foreign languages.
Dar-es-Salaam is the main port of entry for most visitors to not just the region, but to the country as a whole, be it by boat or by plane.
Flights leave Dar es Salaam on an almost daily basis to Mtwara.
You can also catch a weekly ferry from the port at Dar es Salaam to Mtwara. It can be cramped and uncomfortable.
There are daily buses leaving Dar es Salaam that run down the coast through Kilwa and Lindi before arriving at Mtwara.
Basic buses run between all the major towns in the area and smaller daladalas run between the surrounding villages.