Jean-Luc, Deanna, and Keiko: No Naming Language At All
There are certainly situations in which no naming language is necessary: mainstream fiction set in the present, nebulously near-future science fiction, and perhaps even urban fantasy.
Near-Future Names
For choosing near-future names, I use The Baby Name Wizard’s Java NameVoyager. I don’t usually need names from the 20th century, but the NameVoyager covers the entire period. Keep in mind that these are baby names, so adult characters won’t have them until at least twenty years later. See, for example, the roller-coaster history of the name Mariah.
For surnames I usually resort to U.S. census data, which once upon a time also covered first names in a less entertaining fashion than the NameVoyager. The data is not broken down by age.
Similar data can be easily googled for other nationalities and periods.
Far-Future Names
The situation gets murkier the further you get from the present day. The Star Trek premise that every human in the 24th century has an average 20th-century name is difficult to support. Although most names from the time survive, the distribution of 16th century names differed significantly from ours. Yet the approach of choosing modern names at random worked for Star Trek and it can work for you.
Jack McDevitt uses apparently random English names for every time period he writes about, even 10,000 years in the future. While this approach helps draw the reader into an individual novel, it can make it difficult to distinguish between different periods in his stories. If you’d asked me before I started typing this paragraph whether Alex Benedict and Priscilla Hutchins were contemporaries, I probably would have said yes. Google informs me that they are separated by about 9,400 years.
If you’re not sure English would become unrecognizable in 10,000 years, then take look just a thousand years ahead at Justin Rye’s Futurese, or look back 725 short years at Chaucer:
Ye knowe eek that in forme of speche is chaunge
With-inne a thousand yeer, and wordes tho
That hadden prys, now wonder nyce and straunge
Us thinketh hem, and yet thei spake hem so,
And spedde as wel in love as men now do [Chaucer, as quoted by Justin B. Rye]
Alien Names
When faced with some far-future John and Mary, one might be tempted to provide the author with the Federation Standard alibi—that he has translated appropriately futuristic names into pronounceable modern ones for reader convenience. This alibi does not extend to alien names. You should not, under any circumstances, call your aliens Priscilla or Alex or Jean-Luc. This is an area in which a naming language is expected.