I've actually been trying to hammer out a sub-dialect for the 'Spacers to simulate the linguistic effects of isolation. As a 'Space-faring race, they are heavily vested into building and maintaining ships, so I've tried to develop some pilot-like lingo for them; hence, a pilot is called a "Spacecase", and an engineer a "Gearhead", and so on. Also since the internet tends to heavily corrupt normal language in most cases (and the 'Spacers are a highly digitally-oriented society) I've tried to play my characters with a heavy amount of slang and odd wording.
Fun fact: Teminus, the 'Spacer god of nuclear war and launch facilities, derives from a corruption of T-minus.
As for how they sound, I've always imagined various dialects due to their semi-isolation; Fleets are physically separate, mostly communicating via digital means, which would cultivate a wide array of accents. However, when I first made this race they were actually a subtle reference to the Irish (Deoradh, their original name, is modern Irish for "exile"). Hence the strong anti-government and pagan undertones; a subtle allusion for the vast number of rebellions over the 700 years they were ruled by Britain, and Celtic mythos, respectively. Even the "Free State" has been historically been used by many nations, including the predecessor of the Republic of Ireland, as a sign of independence from former rulers.
...And I've sidetracked a bit. Ahem. Anyways, yeah, various dialects I imagine derived from various British Isles dialects. More common dialects than rather than upper-class ones such as the King's English. I also imagine a number of Maritime-style dialects, such as those in Newfoundland, which are actually half-blend of North American and Irish culture/language.
(OOC: See: This and this sample for the difference. )
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Separate from the above post, but relevant to this topic nonetheless. This may be quite useful for helping race writers hammer out how they imagine their species should sound:
http://web.ku.edu/idea/index.htm
This is a database of different dialects and/or accents of the English language. They have douzens if not hundreds of samples of accents from different countries, and even the various dialects each country uses. This might be useful for different factions or nations who wish to give others an example of how they may speak.
Fun fact: The British Isles and North America alone have approximately 50 dialects.