Improve when $LANG is set and expand the number of languages supported

[Tyriar]

Fixes #80072

[go2sh]

@Tyriar Is it possible to add a reference to the tasks.json documentation. I searched nearly two hours, why my LANG="" got overwritten with LANG="de_DE.UTF-8". Its quite annoying as I have to force the locale to English to get the diagnostic matcher working...

[Tyriar]

fyi @alexr00

@go2sh any reason why you don't do export LANG="en_US.UTF-8" in your ~/.bashrc?

[go2sh]

German is my preferred language, so de_DE is okay for normal usage. But the gcc problem matcher only recognizes Error and not Fehler, so for this special case, I'd like the language to be changed. I use a special TaskDefinition with TaskProvider to supply Tasks with a ProcessExecution. So bashrc do not apply.

[Tyriar]

@go2sh I think for your case you're doing the right thing, You can either setLocaleVariables to false (which will be detectLocale to "off" soon from this PR) and handle it yourself or overriding the env just for tasks.

[go2sh]

@Tyriar Thank you. I just wanted to make sure with comment, that the option (either the old or new own) gets mentioned in the documentation (tasks page and api page under the *ExecutionOptions). As extension developer, I got a lot of reports regarding the LANG environment variable and I spent a lot of time reading and debugging the code to find the config option.

Also I like the PR very much because now you have a change to override the var without changing the configuration (as auto is the default compared to true before). I implemented a check in my extension for the old config option to warn the user to enable it, when he tries to override the LANG var.