Scratch

The join [] with [] and [] and [] block

Shift-Click the loop of the R in the Scratch-Logo and select "turn fill screen off".
Click in the white area that appears and click open, then browser.

Go to Scratch-Objects -> ScriptableScratchMorph -> string ops -> concatenate:with:
Copy this code:

concatenate: t1 with: t2 and: t3 and: t4 
    | t5 t6 |
    t5 _ t1 asString , t2 asString.
    t6 _ t3 asString , t4 asString.
    ^ t5 asString asUTF8 , t6 asString asUTF8

Press Alt+A, Alt+V and Alt+S.

Press "class" -> block specs -> blockSpecs and copy this:

('join %s %s' #r #concatenate:with: 'hello ' 'world')

Press Alt+F and Alt+V.
Insert this code after the selected code:

 ('join %s with %s and %s and %s' #r #concatenate:with:and:and: '' '' '' '')

Press Alt+S and close the browser.

Shift-Click the loop of the R again.
Select "turn fill screen off".
Shift-Click the loop another time.
Select "save image for end-user" and "yes".
Start Scratch again.
Go to "Operators".

You now have a block "join [] with [] and [] and []"!