#include <StringConstants.au3> ; to declare the Constants of StringRegExp
#include <Array.au3> ; UDF needed for _ArrayDisplay and _ArrayConcatenate
Local $sRegex = "(?m)(\d{4}-\d{2}-\d{2}\\t)(.*?)(\[\w{2}\]\\t)"
Local $sString = "\n2021-01-12\tThis string is not needed [it]\tBad things\tBad things\n2021-01-12\tThis string is also not needed [en]\tBad things\tBad things\n2021-01-11\tString 1 that is needed! [it]\tString 1 that is needed! is repeated here\tNot interesting here\n2021-01-11\tString 2 that is needed [fr]\tString 2 that is needed is repeated here\tUnnecessary string\n2021-01-11\tString 3 that is needed... [ru]\tString 3 that is needed... is repeated here\tAnother part we're not interested in"
Local $aArray = StringRegExp($sString, $sRegex, $STR_REGEXPARRAYGLOBALFULLMATCH)
Local $aFullArray[0]
For $i = 0 To UBound($aArray) -1
_ArrayConcatenate($aFullArray, $aArray[$i])
Next
$aArray = $aFullArray
; Present the entire match result
_ArrayDisplay($aArray, "Result")
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for AutoIt, please visit: https://www.autoitscript.com/autoit3/docs/functions/StringRegExp.htm