Environment

Windows 10 Education, Build 18362.19h1_release_svc_19h2_rel.190621-1123 Windows Terminal version (if applicable): Latest build from revision 0ce08aff , i.e. after commit 33361698 (but it didn't work either before).

Any other software? -> Testing Mathematica 11.3 kernel, but also reproducible using Wolfram Engine (free DL at official website https://www.wolfram.com/engine/ )

Steps to reproduce

Just open math (or wolframscript when using Wolfram Engine) command and try to enter square brackets or other symbols that require pressing either AltGr or Ctrl-Alt on french keyboard layout.

Expected behavior

The square brackets should appear....

Actual behavior

... but they do not. See the screen-capture. The problem happens when using standard Conhost and also the OpenConsole.exe version. On the contrary, the square brackets are correctly transmitted to the math (or wolframscript) program when using MinTTY from Git4Windows.