Make Language.pipe workers exit cleanly

[danieldk]

Description

Also warn when any worker exited with a non-zero exit code and modify test to ensure that workers exit cleanly by default.

Types of change

Bugfix

Checklist

• I confirm that I have the right to submit this contribution under the project's MIT license.
• I ran the tests, and all new and existing tests passed.
• My changes don't require a change to the documentation, or if they do, I've added all required information.

[svlandeg]

Thanks!