getLangEnvVariable fallback to en_US.UTF-8 too early without checking locale -a

[soiamsoNG]

• VSCode Version: 1.51.0 fcac248
• OS Version: Linux x64 5.8.18-300.fc33.x86_64

Steps to Reproduce:

1. use terminal in container with default LANG=POSIX setting
2. getLangEnvVariable fallback to en_US.UTF-8 without checking locale -a and incorrect set LANG
   in my case locale -a just support below 3. it actually have utf-8 locale in this system.

C
C.UTF-8
POSIX

Does this issue occur when all extensions are disabled?: Yes/No

[jorgelaranjo]

This is a fresh new bug and widespread https://www.reddit.com/r/vscode/comments/jsdwvl/issues_with_internal_terminal_locale/
Also reported #110322