We have $\pi$ and $\aleph_0$ borrowed from Greek and Hebrew alphabets. Are there widely accepted math symbols using non-Latin alphabets or characters other than Greek and Hebrew?
The letter Ш (sha) of the Cyrillic alphabet is widely accepted in theoretical computer science as the symbol for the shuffle product, which gives the shuffle algebra.
The same letter is also used to denote the Tate-Shafarevich group, but I'm not sure if it's really a standard (the letter was introduced by Cassels
only in 1990 in 1962 instead of TS, see below the KCd's comment).
There are several non-alphabetic symbols, the best known is the integral sign $\int$ and the Weierstrass $P$-function $\wp$. To be sure their origins are letters of Latin alphabet, but they are special stylized symbols, and as far as I know there is no computer code for them in the standard sets of computer characters. Strictly speaking they do not belong to any alphabet. $\wp$ imitates Weierstrass handwriting. Symbols $\partial$ for the partial derivative and $\infty$ also belong to this list.
There are also mathematicians who use Cyrillic letters, for example John Milnor used Л for some standard function is hyperbolic geometry, but this can hardly be called "widely accepted". Л is the first letter in Lobachevski's name (Лобачевский). I've seen other Cyrillic letters used, but again this is not "widely accepted".
An interesting case is the "letter" $\nabla$ usually used for the gradient. This is a apparently not a letter from any alphabet, and it is called "Nabla" which is the Greek word for some Phoenician musical instrument. See Nabla symbol. Unlike $\wp$ it is included in Unicode.
It is sometimes asserted that $\varnothing$ for the empty set was introduced by Bourbaki using a Danish and Norwegian letter.
The source is the Weil autobiography, cited in Jeff Miller's collection of the origins of mathematical expressions:
André Weil (1906-1998) says in his autobiography that he was responsible for the symbol:
Wisely, we had decided to publish an installment establishing the system of notation for set theory, rather than wait for the detailed treatment that was to follow: it was high time to fix these notations once and for all, and indeed the ones we proposed, which introduced a number of modifications to the notations previously in use, met with general approval. Much later, my own part in these discussions earned me the respect of my daughter Nicolette, when she learned the symbol Ø for the empty set at school and I told her that I had been personally responsible for its adoption. The symbol came from the Norwegian alphabet, with which I alone among the Bourbaki group was familiar.
The citation above is from page 114 of André Weil's The Apprenticeship of a Mathematician, Birkhaeuser Verlag, Basel-Boston-Berlin, 1992.
The cyrillic letter Ш (sha)is -- for obvious reasons when looking at the graph) also used to denote the "function" (well, it is a distribution if you want to be picky) given by the sum of integral displacements of the Dirac-delta function, see https://en.wikipedia.org/wiki/Dirac_comb