17. Julia (128 bytes)

#v`16 "<" 6/b0\ .q@#;n4"14""
#>3N9@15o|R"12"*^
#=|
print((1/2and 9 or 13)-(0and+4)^1<<65>>62);# =#;print(17)
#gg99ddi2` |1|1+6

There are two ESCs on the last line, one before the first g and one after the 2. This could be golfed more, but things got messy no thanks to V and Pyth.

Prints 1 in Python 3, 2 in V, 3 in Minkolang, 4 in ><>, 5 in Python 2, 6 in SMBF, 7 in Japt, 8 in Retina, 9 in Perl, 10 in Befunge-93, 11 in Befunge-98, 12 in Fission, 13 in Ruby, 14 in Turtléd, 15 in Haystack, 16 in Pyth and 17 in Julia.

Hints:

• The start of the fourth line is Python 2/3, Perl, Ruby. The end is Julia, thanks to #= multiline comments (note that Julia doesn't have and/or).
• V is <ESC>gg99ddi2<ESC>, which is definitely golfable but V is annoying to test on Try it online! since the interpreter is fairly slow.
• Minkolang and Haystack go down at the first v. Befunge-93 and -98 don't, and depend on a b.
• Retina counts the number of spaces and 1s in the fourth line, and V hides in the config for Retina (i.e. before the backtick).
• Per @ETHproduction's hint, Japt uses backticks to hide the majority of the code in a string.
• Fission is R"12"*.
• SMBF has been golfed to <. in the first line, plus the final 6.

5. Python 2 (35 bytes)

#3N.;n4
print('1'if 1/2else'5')
#i2

This program prints 1 in Python 3, 2 in Vim, 3 in Minkolang v0.15, 4 in ><> and 5 in Python 2.

Try It Online beta!

In Python 2, 1/2 is 0, which is a falsy value, which makes Python print 5. In Python 3, 1/2 is 0.5, which is a truthy value, which makes Python print 1.

10. Befunge, 95 bytes

#v02^0;7||"<+0+0+0+<;n4
#v0#@00
#>3N.
#|\w*
#8
#|
#M`
print(None and 9or 1/2and 1or 5)
#jd5ki2

There is a literal ESC character between j and d on the last line (grr, @ais523). It is not included in this code. To get the actual code, please go to the Try it online link.

This prints 1 in Python 3, 2 in Vim, 3 in Minkolang, 4 in <><, 5 in Python 2, 6 in SMBF, 7 in Japt, 8 in Retina, 9 in Perl, and 10 in Befunge.

This code shares * with Retina and . with Minkolang and SMBF.

Try it online

Explanation

Actual program

#v02^
    @
    .
    *



    t
    5
#v02^

The last line was written for clarity (Befunge playground is cyclic.)

#

Trampoline, skips v

02^

Push 0 and then 2 in stack and go up.

5t*.@

Push 5, no-op, multiply two elements in stack (2 and 5), print, end program.

11. Befunge 98, 102 bytes

#v;2^0;7||"<+0+0+0+<;n4
#v0#_q@
#>3N.
#|\w*
#8  ^1b0<
#|
#M`
print(None and 9or 1/2and 1or 5)
#jd5ki2

Prints:

• 1 in Python 3
• 2 in Vim - This takes quite a while to output for some reason...
• 3 in Minkolang v0.15
• 4 in ><>
• 5 in Python 2
• 6 in SMBF
• 7 in Japt
• 8 in Retina
• 9 in Perl
• 10 in Befunge 93
• 11 in Befunge 98

To be perfectly honest, I have no clue why the Vim code takes 1 min to output. Also, no clue how Retina works.

Explanation:

#v          Skips the v, which would send the IP down
  ;         Unlike '93, where ; is a no-op, '98 skips to the next ;
            and doesn't execute anything in between
   2^0;     Not executed, unlike Befunge 93
       7|   Pushes 7 onto the stack, and then sends the IP up, because 7 is not 0
n0b1        n clears the stack, and #s are pushed until the stack is [0, 11, 1
    *.      multiplies the top 2 values of the stack to give 11, and prints it (yay!)
      _     Sends the IP right, because the top value of the stack is 0
       q    Ends the program (no-op for '93, which continues to @)

Things to note:

• The 0 next to the b isn't strictly necessary in the code's current state, and the stack has been cleared. It can be removed if necessary, but allows for other stack manipulation beforehand as part of a possible future program.
• The _q@ is there as part of Retina (It doesn't work without it, don't ask me why). The addition of q also lets the '98 code run a t operation, which splits the IP (along with making the Retina program print 8 instead of 7)
• The _ is not a simple > because that would mess the SMBF part up.

Edit: Just realized that the _q@ should probably be @00 (Where 0s can be ~any char) to make the program more flexible in the future. I'm too lazy (and tired) to change all the links right now though. Will get around to it eventually...

Edit 2: I Didn't expect 6 more answers this quickly. I guess it's staying as is. Great job everyone!

20. Prelude, 167 bytes

#v`16 "<" 6/b0\ .q@#;n4"14""
#>3N9@15o|R"12"*^*ttt*~++%
#=|
print((1/2and 9 or 13)-(0and+4)^1<<65>>62);#35(99999+++++!) =#;print(17)
#       ~nJ<
#
#gg99ddi2` |1|1+6

Literal ESC characters in the same place as in the previous submissions (between the # and g, and between the 2 and `, on the last line), because you can't take Vim out of insert mode with printable characters.

This program prints 20 in Prelude, 19 in Reng (testable here), 18 in Cardinal, 17 in Julia, 16 in Pyth, 15 in Haystack, 14 in Turtlèd, 13 in Ruby, 12 in Fission, 11 in Befunge-98, 10 in Befunge-93, 9 in Perl, 8 in Retina, 7 in Japt, 6 in SMBF, 5 in Python 2, 4 in ><>, 3 in Minkolang, 2 in Vim/V, 1 in Python 3, and a partridge in A Pear Tree.

The existing code pretty much cancels itself out in Prelude, consisting only of while loops with falsey arguments and some stack manipulation on stacks we don't care about. Even better, there's a spot in the code that's a comment in all the languages that have them (between the # and =# of the previous submission). The hard part of fitting Prelude into this was generating numbers with only one stack and without blowing up the byte count. This program uses a loop that adds 45 to every stack element and outputs it as ASCII, thus by placing a 5 above a 3 on the stack, we get 20 as output. (Neatly, 20 is an easier number to output than 19 is in Prelude, so answer 19 being posted actually helped me a bit.)

3. Minkolang v0.15 (26 bytes)

#>>>>>>>>v
print(1)#>3N.i2

This program prints 1 in Python 3, 2 in Vim, and 3 in Minkolang v0.15

I hope I don't mess things up by introducing a 2d language

Try it online!

Explanation

#                     stops program from moving through time (really does nothing)
 >>>>>>>>             I can't use a space because then the program will move through time
         v            go down
         >            go right
          3N.         Outputs 3 and end program
                      Anything afterward is ignored since program has ended

Vim somehow ignores Minkolang, so that's good

And there really wasn't a problem with Python since it ignores the comments #

Next...

For the next language, I suggest something like ><> since # acts as a reflector (so that the direction will change to left and it will wrap to all the way in the right) so you can add code that can be ignored by other languages

15. Haystack (141 bytes)

#v;2^0;7||"<+0+0+0+<*!2'!1'L#'1r'4;n4
#v0#_q@
#>3N.15o|1
#|\w*
#8  ^1b0<
#|
#M`
print ((0 and'13')or(None and 9 or 1/2 and 1 or 5))
#jd5ki2

Note: there is an ESC after o in the third line and after j in the last line

This prints 1 in Python 3, 2 in Vim, 3 in Minkolang, 4 in <><, 5 in Python 2, 6 in SMBF, 7 in Japt, 8 in Retina, 9 in Perl, 10 in Befunge, 11 in Befunge-98, 12 in Fission, 13 in Ruby, 14 in turtlèd, and 15 in Haystack.

Try it online!

Explanation

#v                           go down
 v
 >                           go right
  3N.                        does nothing important
     15o|                    outputs 15 and ends program
                             there is an <ESC> after 'o' since 'o' in Vim enters insert mode
         1                   I added this to satisfy Retina

4. ><> (29 bytes)

#>>>>>>>>v;n4
print(1)#>3N.i2

This program prints 1 in Python 3, 2 in Vim, 3 in Minkolang v0.15 and 4 in ><>

Try it Online!

Code ran

#             - change direction to left
            4 - add 4 to stack
           n  - print as a number
          ;   - end the program

Yet another 2D language.

Has no effect on Minkolang as it adds characters after the direction changes, gets ignored by Vim for some reason. # is a comment in Python so no change their either.

6. SMBF, 45 bytes

#v<++++<;n4
#>3N.
print('1'if 1/2else'5')
#i2

Try it online

This program prints 1 in Python 3, 2 in V, 3 in Minkolang v0.15, 4 in ><>, and 5 in Python 2.

SMBF (aka Self-modifying Brainfuck) uses <++++<>.. The pointer is moved left (to the last character of the source code), and the cell is incremented four times then printed.

21. Nim (161 bytes)

#v`16/"<"6/b.q@#;n4"14""
#>3N6@15o|> ^*ttt*~++ %
#=~nJ<R"12";
#[

print((1/2and 9 or 13)-(0and+4)^1<<65>>62)#46(89999+++++!)=#print(17)#]#echo 21
#8dggi2` |1|6

Two <ESC>s, between 8d and between 2` on the last line. You can tell that my previous one was golfed in a hurry, because I woke up this morning and realised I could take a bunch more off. I had 152 bytes but that seems to only work in Perl 5.24.0, so in the interest of compatibility with TIO I've kept the original expression for now.

Prints 1 in Python 3, 2 in V, 3 in Minkolang, 4 in ><>, 5 in Python 2, 6 in SMBF, 7 in Japt, 8 in Retina, 9 in Perl, 10 in Befunge-93, 11 in Befunge-98, 12 in Fission, 13 in Ruby, 14 in Turtléd, 15 in Haystack, 16 in Pyth, 17 in Julia, 18 in Cardinal, 19 in Reng, 20 in Prelude and 21 in Nim.

Note that Nim on ideone.com uses version 0.11.2, which is a tad too old, since this program relies on #[ ... ]# multiline comments added in early 2016.

Thanks to Cardinal's Windows interpreter, my workflow now consists of two laptops and a Python http.server in between.

Edit — some more hints:

• The 8 at the start of the last line is to set Retina's limit to the first 8 matches, otherwise without it Retina would output 2. Note that this means the final line regex only needs to match at least 8 times in the second last line now, as opposed to exactly 8 — during my meddling I modified Prelude to get Retina right, but it turned out that was unnecessary in the end.
• The mismatched quote at the end of the first line is so that Pyth doesn't complain about invalid syntax for the rest of the code.
• If you modify the second line you might have to change the 6@ for Minkolang, which makes the pointer jump 6 spaces to land on the ^.
• There's a pair of [] now, so SMBF needs to be on a 0 cell before it hits the [, or alternative the interior needs to clear the cell.

There's probably more to golf (even now I see a stray space before the % for Cardinal), but I should really stop golfing in the wee hours of the morning.

13. Ruby (129 bytes)

#v;2^0;7||"<+0+0+0+<*!2'!1'L;n4
#v0#_q@
#>3N.
#|\w*
#8  ^1b0<
#|
#M`
print ((0 and'13')or(None and 9 or 1/2 and 1 or 5))
#jd5ki2

Please note the literal Esc character on the last line between the j and d, as per ais523's Perl answer.

Try it online!

This prints 1 in Python 3, 2 in Vim, 3 in Minkolang, 4 in <><, 5 in Python 2, 6 in SMBF, 7 in Japt, 8 in Retina, 9 in Perl, 10 in Befunge, 11 in Befunge-98, 12 in Fission and 13 in Ruby.

Just a minor modification to the existing print statement to abuse the fact that 0 is truthy in Ruby. I had to add some spaces to the other statements to make it parse correctly.

16. Pyth (159 bytes)

#v\;2^0\;7||"<+0+0+0+<*!2'!1'L#'1r'4;n4
#v0#_q@
#>3N.15o|1
#|\w*
#8  ^<1b0 <
#|
#M`
print ((0 and'13')or(None and 9 or 1/2 and 1 or 5))
#"07|5//00;16 "jd5ki2

Note: there is an ESC byte (0x1B) after the o in the third line and after the j in the last line.

This was quite a fun experience. Japt and Pyth are both golfy languages, but Japt is infix and Pyth is prefix, and Pyth auto-requests input and fails if arguments are missing.

Before the Haystack answer I had an almost-working solution using #, which gets a char code in Japt and loop-until-error in Pyth. Pyth happens to be very useful in polyglots, since the common comment char # essentially works as an error silencer.

When I got home I managed to find a this piece of code that worked in both using //, which works as a comment in Japt and two divisions in Pyth. Then it was just a matter of getting the Befunges to route correctly.

This is very unlikely to be optimal, but it's good enough for now. I tried to test them all, but I'd highly appreciate someone double checking that the outputs match.

Prints 1 in Python 3, 2 in V, 3 in Minkolang, 4 in ><>, 5 in Python 2, 6 in Self-Modifying Brainfuck, 7 in Japt, 8 in Retina, 9 in Perl, 10 in Befunge(-93), 11 in Befunge-98, 12 in Fission, 13 in Ruby, 14 in Turtléd, 15 in Haystack, and

16 in Pyth.

Explanation

What Pyth sees here is:

#v\;2^0\;7||"string
multiline
string"07|5//00;16 "string

This translates to the following pseudocode:

while no errors occur:
    evaluate ";"
    print 2
    print 0 to the power ";"
    print 7
    print "string\nmultiline\nstring" or 0 or 7
    print 5 or 0 divided by 0 divided by (missing)
print 16
do nothing with "string"

The first loop exits on trying to evaluate ; which isn't a valid expression. Then Pyth just prints 16.

14. Turtlèd (135 bytes)

#v;2^0;7||"<+0+0+0+<*!2'!1'L#'1r'4;n4
#v0#_q@
#>3N.
#|\w*
#8  ^1b0<
#|
#M`
print ((0 and'13')or(None and 9 or 1/2 and 1 or 5))
#jd5ki2

This prints 1 in Python 3, 2 in Vim, 3 in Minkolang, 4 in <><, 5 in Python 2, 6 in SMBF, 7 in Japt, 8 in Retina, 9 in Perl, 10 in Befunge, 11 in Befunge-98, 12 in Fission, 13 in Ruby and 14 in Turtlèd.

First line added #'1r'4 near the end of line, Turtled takes #[string]# as string input then 'X places the value of x on the grid, r moves right 1 space on the grid. The value on the grid is printed at the end of the program implicitly.

Try it Online

Link to Turtled docs

2. Vim (11 bytes)

print(1)#i2

This program prints 1 in Python 3, and 2 in Vim.

Just to get the ball rolling and to throw my favorite language into the mix early on. :)

It's a very straightforward answer.

print(1)#

just so happens to be a NOP in vim. (lucky for me) Then i2 enters insert mode and inserts a '2'. You can try vim online here

Of course, in python

print(1)

prints '1', and

#2

is a comment.

23. Hexagony, 186 bytes

Sorry if this messes up plans...

#v`16/"<"6/b.q@"(::):::  (22)S#;n4"14"
#>3N6@15o|> ^*ttt*~++~~~%
#=~nJ<R"12";
#[

print((1/2and 9 or 13)-(0and+4)^1<<65>>62)#46(89999+++++!)=#print(17)#0\32=""<0]#echo 21
#8␛dggi2␛` |1|6

␛ is used to represent a literal ESC character.

Prints:

23 in Hexagony, 22 in Underload, 21 in Nim, 20 in Prelude, 19 in Reng (testable here), 18 in Cardinal, 17 in Julia, 16 in Pyth, 15 in Haystack, 14 in Turtlèd, 13 in Ruby, 12 in Fission, 11 in Befunge-98, 10 in Befunge-93, 9 in Perl, 8 in Retina, 7 in Japt, 6 in SMBF, 5 in Python 2, 4 in ><>, 3 in Minkolang, 2 in Vim/V, and 1 in Python 3.

To get to the unlinked languages, click the change language button in the upper right of the Hexagony link.

Hexagony isn't readable (at ALL) in this format. We need to look at it in hexagonal form.
Note that the 2 ESC characters have been replaced with ␛s so you can see them - they are ignored, so there are no others in the program:

        # v 1 6 / " < " 6
       / b . q @ " ( : : )      A lot more readable, right?? No?
      : : : ( 2 2 ) S # ; n
     4 " 1 4 " # > 3 N 6 @ 1
    5 o | > ^ * t t t * ~ + +
   ~ ~ ~ % # = ~ n J < R " 1 2
  " ; # [ p r i n t ( ( 1 / 2 a
 n d 9 o r 1 3 ) - ( 0 a n d + 4
) ^ 1 < < 6 5 > > 6 2 ) # 4 6 ( 8   | Note that the 0s below can be replaced
 9 9 9 9 + + + + + ! ) = # p r i    | With anything (except "`" or " "), 
  n t ( 1 7 ) # 0 \ 3 2 = " " <     V as far as Hexagony is concerned
   0 ] # e c h o 2 1 # 8 ␛ d g
    g i 2 ␛ | 1 | 6 . . . . .    <-- the ␛ represents an esc
     . . . . . . . . . . . .         character
      . . . . . . . . . . .
       . . . . . . . . . .       A "." is a no-op
        . . . . . . . . .
                ^
                | Mirror wraps to here, going NW

For those unfamiliar with Hexagony, There are 6 IPs, which start at the 6 corners. Only 1 is active at a time, and are switched by using #][. The memory model isn't that important to this program, but might be necessary to understand in the future. All that you need to know is that 1 int is stored in a "memory edge" (ME for short), and '"}{ change the ME that is active.

\/|_>< are mirrors that control program flow.

This is how it works:

First line executed:

#       A no-op (sets active IP to 0, the currently active one)
 v      letter chars set the ME to their ASCII value - so ME is now 118
  16    Like Labyrinth, 0-9 multiplies ME by 10 and is added - ME now 11816
    /   A mirror that sends IP going NW by wrapping to the bottom

The bottom (snippet flipped vertically so you can read up to down):

    .   
   .    A series of no-ops. The IP is going NW now,
  .     because of the mirror on the top.
 .
|       Another mirror. This one sends the IP NE, into the h
 h      sets the ME to 104, the ASCII value for h
  #     104 % 6 == 2, so IP 2 is now active instead of 0

The right edge:

        8  IP #2 is moving SW, starting in the right corner 
       i   Sets the ME to 105
      <    Mirror. Sends the IP going due West
    ""     These change the Active ME - just know that the new edge is 0
   =       Changes the MP (more in specs) - effectively a no-op used to fill space
\32        pushes 23, and mirrors up NE to the !

The last bit of relevant code:

!          Prints the current value of the ME as an int. Success!
 20(R~     Does things to the ME - irrelevant now
      @    Ends the program!

Things to note:

• Hexagony drops all s and `s before executing, so any changes to those will not affect Hexagony
• I needed to pad the code so that it would be interpreted as a 9 length hexagon, instead of an 8th - be careful golfing below 169 or above 217 relevant characters
• Because of this, the ~~~ and the 2 0s at the end can be changed at no harm to the code
• The ="" just moves the ME away from the previous one so that a new ME can be modified. They can be replaced with other characters that do the same thing at no harm to the hexagony program ('s, for example)
• This is technically not comlient with the Befunge 93 specs, because it limits the bounding box of the code to 80 by 25 chracters. However, Most interptreters ignore this spec (like TIO), So I don't personally think it's that big of a deal. If you do, feel free to leave a comment. (If enough really want me to change it, then I will try)
• Hope it's not too hard now.

7. Japt (50 bytes)

#v;7||"<++++<;n4
#>3N.
print('1'if 1/2else'5')
#i2

Man, it was fun to fit Japt in there. Hopefully it didn't kill anyone's plans...

Test it online!

This program prints 1 in Python 3, 2 in V, 3 in Minkolang v0.15, 4 in ><>, 5 in Python 2, and 6 in SMBF.

How this works: #v; takes the char code of v, or 118. Then 7|| returns the logical OR of 7 and the rest of the code, which is wrapped in a string with " to avoid any syntax errors. The result, 7, is automatically sent to STDOUT.

For future polyglotters, " can be changed to ` at no penalty to the Japt program (though I'm not sure about the others).

8. Retina, 70 bytes

#v;7||"<+0+0+0+<;n4
#>3N.
#|\w*
#8
#|

#M`
print('1'if 1/2else'5')
#i2

Try it online

This program prints 1 in Python 3, 2 in V, 3 in Minkolang v0.15, 4 in ><>, 5 in Python 2, 6 in SMBF, and 7 in Japt.

Screw creating hyperlinks to interpreters. That's going to take way too much time. It's up to the poster and anyone creating new answers to test it yourself.

Explanation:

#v;7||"<+0+0+0+<;n4     # replace every empty string with "#>3N."
#>3N.
#|\w*                   # replace words chars with "#8"
#8
#|                      # remove all "#". The "|" is something I could've golfed off.

#M`                     # match all places between characters (finds 8)
print('1'if 1/2else'5') # replace something that won't be found. noop
#i2

19. Reng, 152 bytes

#v`16 "<" 6/b0\ .q@#;n4"14""
#>3N9@15o|R"12"*^*ttt*~++%
#=|
print((1/2and 9 or 13)-(0and+4)^1<<65>>62);# =#;print(17)
#       ~nJ<
#
#gg99ddi2` |1|1+6

I added another #\n so that retina would cooperate. Here's how it works:

# redefines v to push 0, the default TOS. Then, it negates the TOS (`), pushes 1 and 6, the character of <, pushes 6 again, and mirrors upwards with /, colliding with the other `, which negates the 6. Then, it hits the <, pushes J (base 36 for 19), then outputs it as a number, finally terminating (~).

Escapes in between 2 and `; and # and g.

1. Try it online!—Python 3
2. Try it online!—V
3. Try it online!—Minkolang
4. Try it online!—><>
5. Try it online!—Python 2
6. Try it online!—SMBF
7. Ethproductions—Japt
8. Try it online!—Retina
9. Try it online!—Perl
10. Try it online!—Befunge 93
11. Try it online!—Befunge 98
12. Try it online!—Fission
13. Try it online!—Ruby
14. Try it online!—Turtléd
15. Try it online!—Haystack
16. Try it online!—Pyth
17. Try it online!—Julia
18. Try it online!—Cardinal
19. JSFiddle—Reng

9. Perl, 84 bytes

#v;7||"<+0+0+0+<;n4
#>3N.
#|\w*
#8
#|

#M`
print(None and 9or 1/2and 1or 5)
#j␛d5ki2

There's a literal ESC character in the actual code between the j and d; it has been replaced with a ␛ here for visibility.

This prints 1 in Python 3, 2 in Vim (tested locally, but here's a link for the very similar language V), 3 in Minkolang, 4 in <><, 5 in Python 2, 6 in SMBF, 7 in Japt, 8 in Retina, and 9 in Perl.

Let's get some more exoteric languages in, via abusing arithmetic that works differently in different languages. (None is falsey in Python but truthy in Perl, and and/or chains work the same way in both languages.)

Apart from Python, I also had to change the vim code. Instead of making it into a series of no-ops, I just let it insert junk, then deleted the junk again at the end.

18. Cardinal, 137 bytes

#v`16 "<" 6/b0\ .q@#;n4"14""
#>3N9@15o|R"12"*^*ttt*~++%
#=|
print((1/2and 9 or 13)-(0and+4)^1<<65>>62);# =#;print(17)
#gg99ddi2` |1|1+6

Literal escape chars between # and g, and 2 and `.

Prints:

• 1 in Python 3
• 2 in V
• 3 in Minkolang
• 4 in ><>
• 5 in Python 2
• 6 in SMBF
• 7 in Japt
• 8 in Retina
• 9 in Perl
• 10 in Befunge 93
• 11 in Befunge 98
• 12 in Fission
• 13 in Ruby
• 14 in Turtléd
• 15 in Haystack
• 16 in Pyth
• 17 in Julia
• 18 in Cardinal (No online interpreter, but the specs are here)

Edit: Fixed esc character between o and | - don't know why it was there in the first place.

22. Underload (stringie), 173 bytes

#v`16/"<"6/b.q@"(::):: :(22)S#;n4"14"
#>3N6@15o|> ^*ttt*~++ %
#=~nJ<R"12";
#[

print((1/2and 9 or 13)-(0and+4)^1<<65>>62)#46(89999+++++!)=#print(17)#]#echo 21
#8dggi2` |1|6

As before, there's a literal ESC character immediately after each of the 8 and 2 on the last line.

This program prints 22 in Underload, 21 in Nim, 20 in Prelude, 19 in Reng (testable here), 18 in Cardinal, 17 in Julia, 16 in Pyth, 15 in Haystack, 14 in Turtlèd, 13 in Ruby, 12 in Fission, 11 in Befunge-98, 10 in Befunge-93, 9 in Perl, 8 in Retina, 7 in Japt, 6 in SMBF, 5 in Python 2, 4 in ><>, 3 in Minkolang, 2 in Vim/V, and 1 in Python 3.

stringie is the Underload interpreter used by Try It Online! Fortunately for polyglotting, it ignores non-command characters rather than crashing on them, so the main thing to ensure is that there are enough stack elements that we don't get an empty stack crash (done here with (::):::; the code probably doesn't actually need that many colons, but I added them anyway as padding to remove awkward vertical alignments). Because it had to appear fairly early (it needs to be before any instances of aS^:*~!), I placed the Underload code on the first line; thanks for Sp3000 for suggesting a place where it would fit safely.

I needed to leave an additional space on the first line because Cardinal doesn't like : lined up with %; I also needed to structure the Underload code to avoid parentheses lining up with each other vertically (which Prelude dislikes). Pyth was the hardest language to get working, and I needed to resort to advice from Sp3000 there (who suggested moving the double quotes around; this combination works). In an earlier version of the code, the Underload was further to the right, but that got in the way of Turtlèd.

The space immediately after the Underload (i.e. after the S of (22)S should still be safe; the Underload doesn't change that. In order to avoid causing problems for Underload, ensure that your code has matched parentheses, avoids S, and isn't intelligible enough as Underload code to cause problems in its own right. (::) has a tendency to breed once it's placed on the stack (I intentionally wanted to write the Underload in a fairly robust way to make continuing the chain easier), so most random sequences of non-S characters will be safe from here, but it's possible to defeat the "ignore the rest of the program" if you try hard enough. If you need an S for some reason, try ensuring that some pair of parentheses captures it; that'll cause Underload to treat it as data rather than code and avoid producing stray output.

1. Python 3 (8 bytes)

print(1)

This program prints 1 in Python 3.

Starting this off with Python 3 because I know it's good for polyglots and can be taken in a number of different directions (also, I wanted to ensure that the first answer was in a relatively normal language, rather than an absurd esolang that's hard to polyglot with).

12. Fission (110 bytes)

Just adding yet another 2d lang... Streak of 3 2d-langs in a row, let's keep it moving folks!

#v;2^0;7||"<+0+0+0+<*!2'!1'L;n4
#v0#_q@
#>3N.
#|\w*
#8  ^1b0<
#|
#M`
print(None and 9or 1/2and 1or 5)
#jd5ki2

This prints 1 in Python 3, 2 in Vim, 3 in Minkolang, 4 in <><, 5 in Python 2, 6 in SMBF, 7 in Japt, 8 in Retina, 9 in Perl, 10 in Befunge, 11 in Befunge-98, and 12 in Fission.

Try it online!

Explanation

The only important piece of code is the first line

                These are the important bits
                    >------<
#v;2^0;7||"<+0+0+0+<*!2'!1'L;n4
                           ^
                   we start here by creating an atom moving Left
           (I could not use R for Right since that means Replace in Vim)

                       1'          sets the atom's mass to the ASCII value of '1'
                      !            outputs the atom's mass (as a character) 
                    2'             sets the atom's mass to the ASCII value of '2'
                   !               outputs it
                  *                program terminates

Next...

If Fission is causing trouble, remember, you can move the Fission code anywhere you want, since the start of the program is only identified by the commands that create atoms, and the program ends whenever the atoms are destroyed.

You can also change the atom's start direction to suit your needs, R for Right (but Vim will interpret that as Replace), U for Up, D for Down (or Deletes entire line in Vim, can be useful).

24. Numberwang, 212 bytes

#v`16/"<"6/b.q@"(::):::  (22)S#;n4"14"
#>3N6@15o|> ^*ttt*~++~~~%
#=~nJ<R"12";
#[

print((1/2and 9 or 13)-(0and+4)^1<<65>>62)#46(89999+++++!)=#print(17)#0\32=""<0]#echo 21
#8␛dggi2␛` 07775340574099127127003993|1|6

Note: there are two literal ESC characters in this code, before and after dggi2 in the last line. They have been replaced with ␛ for visibility.

This code prints 24 in Numberwang, 23 in Hexagony (test it here), 22 in Underload, 21 in Nim, 20 in Prelude, 19 in Reng (here), 18 in Cardinal, 17 in Julia, 16 in Pyth, 15 in Haystack, 14 in Turtlèd, 13 in Ruby, 12 in Fission, 11 in Befunge-98, 10 in Befunge-93, 9 in Perl, 8 in Retina, 7 in Japt (here), 6 in SMBF, 5 in Python 2, 4 in ><>, 3 in Minkolang, 2 in Vim/V, and 1 in Python 3.

To test it, take only the digits (non-digit characters are ignored), do the following replacements, and use the Brainfuck interpreter (here's a Numberwang to BF translator):

{"6[digit]" -> "+++ ... (length digit)", "5[digit]" -> "--- ... (length digit)"}

Then:

{"0" -> ">", "1" -> "<", "9" -> "+", "2" -> "-", "3" -> ".", "8" -> ",", "4" -> "[", "7" -> "]"}

The actual code (translated to BF):

<++++++--[<[.+--<-+<.>[<+++++++[++++++++++++<]>.->-<,->]]]---[>-------[>++<-]<-]>>.++.<6

Try it!

Things to note

• The 4s and 7s must match up (They are brackets in Numberwang). I added three 7s in the last line for that reason.

• There is an extra 6 (before 777 in the last line) to make Hexagony work.

• You might go insane while adding another language.