Sharing (characters) is Caring!
20 languages

Using  ()-#*.05;=&gt;^Vefikloqrst (24 characters) so far:

let f l=floor(l**0.5);;       OCaml
let f l=floor(l**0.5)         F#
f(l)=floor(l^.5)              Julia
f(o)=floor(o^.5)              PARI/GP
s^+&gt;5 0&gt;5 0*.5l               Pyth
(* **.5).floor                Perl 6
floor.(**0.5)                 Haskell
flr.(tt ^.5)                  Wonder
l=&gt;l**.5^0                    JavaScript
l-&gt;l**.5^0                    Cheddar
.5^5*5f                       Pyke
(isqrt)                       Maple
ri.5#i                        CJam
isqrt                         Common Lisp
0.5^k                         MATL
*.5^0                         Jelly
*.^0                          M
t0^                           05AB1E
q f                           Japt
r#                            Pushy
V-                            gs2