Werk #7330: Fix confusions when working with localized shell environments

When switching to the site user context we now enforce a non localized environment. The reason for this configuration is that the parameters and outputs of the monitoring plug-ins are localized. If they are called from the core, they are always language-neutral. During manual testing, the plugins may behave differently depending on the localization of the user's environment variables. This can lead to confusion during tests.

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