The chat about Sai's name legalization and mononymy led
me to wonder about the slightly more OT subject of
naming customs in conlangs and concultures. It so
happens that several of my concultures have practiced
mononymy, including two of my recently active ones.
This is arguably a function of the fact that they have
been thought to be non-modern in various senses of the
word, though there is of course no real correlation
between polynymy and non-modernity in natcultures, even
if the tendency towards polynymy probably has increased
with modernity.

Sohlçan have only one name, tho that may be extended
with nicknames, modifiers and patronymics as needed to
characterize or distinguish between namesakes (cf. the
Ptolemies! :-). Names are meaningful and usually
already compounds similar to Greek, Indo-Iranian and
Germanic names. As might be expected nicknames are
often a clipping of the full name, and if so not used
alongside it. Phonological alterations alla James > Jim
are pretty common in such nicknames.

Pwrwxia Twas also have only one name, often derived
from an Indo-Aryan name, and often clipped to conform
to the native pattern with mono- and bisyllabic words,
though phonological change may have shortened down the
Indic name regularly, as _Kalyāṇa_ > E.MIA _Kaliyāṇa_
\> Euia Twas _Klián_ /kʎan/.

Those of my conlangs which are set in more or less
modern Europe, or a modern Europe in a parallel
universe, generally follow the First (Middle(s)) Last
pattern. In Slevan I added a twist, so that first names
usually were saints' names which had only been adapted
to native phonology while surnames were (also) Roman
nomina gentilia or cognomina which had gone through
regular sound change, so that someone may be named
_Benedict Benedjec_ for example, although having
etymologically tautologous names wasn't any rule.

Rhodrese names follow the general Romance saint's
name(s) + occupational or geographical or again saint's
name pattern, with most surnames and many first names
reflecting Rhodrese sound changes, and many Germanic
names being derived from an East Germanic language
("Burgendish") similar to Gothic, rather than a West
Germanic language.

In the same universe as Rhodrese Scandinavians,
Englishmen and Scotsmen (and -women) use patronymics in
addition to surnames much as Russians do and Scandi-
navian nobility did OTL, because thats what I wish had
happened OTL. So someone may be called _Edward Erickson
Smyþ_ or _Eadyþ Fredricksdauhter Smyþ_, where the
middle part is not a name, but only an indication of
one's father's name, and e.g. doesn't change when one
is married. The son of the abovementioned pair might be
called _Erick Fredrick Edwardson Smyþ_.

What about others' conlangs/-cultures?