Fix option name in docs

[MountainCode]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and couldn’t find anything (or linked relevant results below)
• If applicable, I’ve added docs and tests

Description of changes

The documentation says there's an option named lang, but it's actually named language.

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (6cc848a) to head (5f4e9d8).
Report is 4 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff            @@
##              main       #15   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            2         2           
  Lines          181       145   -36     
=========================================
- Hits           181       145   -36     

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[wooorm]

Thank you! :)