I finally found comprehensive answers to this question. The difference between essere and stare for location actually exist in the "official" (standard/supra-regional) Italian language.
tl;dr. For location:
Stare -> Longer time, more persistent, usual place (think as in "Stay")
Essere -> At that moment, more ephemeral (think as in "is, right now")
However, in other cases that are not related to location, these connotations might differ [2, 3, 4], as in the examples below:
- To comment that "he is tall", you'd say "Lui è alto", for example, even though being tall is quite persistent, IMO;
- And to say things in the Gerund tense, that "he is walking", for example, we would say "Lui sta camminando".
Lastly, using stare interchangeably with essere is a colloquialism that comes from the southern region of Italy [1].
Excerpt from Duolingo's forum [1], which is based on another reference:
(...)
The habit of substituting stare for essere is of southern origin;
this strong regional character must be avoided in official and formal
uses. With family and friends, instead, you can stay (stare) more relaxed.
(...)
The following considerations are valid for the national language, not
for regional Italian (in which variable uses apply).
In the sense of "being in a given place", referring to objects, there
is a nuance between the two verbs: essere expresses the location with
reference to the moment of enunciation, while stare denotes the usual
location; compare these two sentences:
(1) The scissors are (sono) in the first drawer to the right of the
sink [where they are now, not necessarily always]. (2) The scissors
are (stanno) in the drawer to the right of the sink [where they are
normally placed]. NB. THIS IS DUO'S USAGE HERE.
Referring to people, the verb stare, in modern neutral use - different,
in part, from past uses - generally has the sense of "staying", "residing",
or indicates the posture, or, of course, the state of health. Then there are idiomatic
expressions, unalterable.
For example these two sentences have a slightly different meaning:
Sono contento di essere qui = "I'm happy to be here [at this precise
moment]"; Sono contento di stare qui = "I'm happy to be here
[always]". The first sentence expresses the place in space and time;
in the second, it emphasizes instead permanence in the place of which
we speak (so that, invited to dinner at a friend's house, I would
always use the first: the second could be misinterpreted by some
touchy soul).
The relations between the two verbs are complex, and not always clear,
also because of regional differences. But phrases like Dove stai? (in
the sense of "Where are you?") or Non ci sta nessuno (for "No one is
present") are not acceptable in supra-regional Italian.
Sources
- https://forum.duolingo.com/comment/630889/La-lampada-sta-sopra-il-tavolo
- https://www.youtube.com/watch?v=cdDFrduKC3w (for comparison with Portuguese verbs)
- Sister that lived in Italy for a couple years
- Google Ngram Viewer