I doubt Steam could choose any forced option that would work in all situations so just leaving it unchanged is probably the best way to go.
You can change the launch parameters for a game to set it to whatever you prefer.
its not a parameter its an environment variable. Will that still work?
And i actually think the opposite of what you said is true. Most games/languages are build on C behavior not national locales.
You can set environment variables on launch, or you could change the launch to run a script.
Nothing extracted yet.
some games require an international LC_ALL setting to work.
For example Planet Explorers. And there are plenty of others games that get bugged out when they are launched with some locale settings the game isnt designed for.