• Clojure

(def s (apply str (repeat n v)))

• Clojure

(def s (clojure.string/join "" (repeat n v)))

• Ada

use Ada.Strings.Fixed;
S : constant String := N * V;

• C

char *s = calloc(strlen(v) * n + 1, 1);
for(int i = 0; i < n; ++i) strcat(s, v);

• C++

s.reserve(v.size() * n);
for (size_t i = 0; i < n; ++i)
  s.append(v);

• C#

string s = string.Create(v.Length * n, (v, n), static (span, state) =>
{
    var (v, n) = state;
    var originSpan = v.AsSpan();
    for (var i = 0; i < n; i++)
    {
        var subSpan = span[(i * originSpan.Length)..];
        originSpan.CopyTo(subSpan);
    }
});

• C#

var s = string.Concat(Enumerable.Repeat(v, n));

• C#

var sb = new StringBuilder();
for(var i = 0; i < n; i++)
	sb.Append(v);

var s = sb.ToString();

• Dart

var s = v * n;

• Elixir

s = String.duplicate(v, n)

• Erlang

S = lists:concat(lists:duplicate(N, V)).

• Fortran

character(len=:), allocatable :: s,v
integer :: n
s = repeat(v,20)
write (*,'(A)') s

• Go

s := strings.Repeat(v, n)
fmt.Println(s)

• Haskell

s = concat $ replicate n v

• JS

const s = v.repeat(n)

• Java

for (int i=0;i<n;i++){
          s = s+v;
      }
System.out.println(s);

• Java

String s = generate(() -> v)
    .limit(n)
    .collect(joining());

• Java

String s = v.repeat(n);

System.out.println(s);

• Kotlin

val s = v.repeat(n)
println(s)

• Lisp

(do ((i 0 (+ i 1 )))( (= i n) s)
  (setf s (concatenate 'string s v)))

• Lua

s = string.rep(v, n)

• PHP

$s = str_repeat($v, $n);
echo $s;

• Pascal

s := DupeString(v, n);
writeln(s);

• Pascal

s:= '';
for i := 1 to n do s := s + v;
writeln(s);

• Perl

my $s = $v x $n;

• Python

s = v * n

• Python

s = ''.join(repeat(v, n))

• Ruby

s = v * n

• Rust

let s = v.repeat(n);