en-US means U.S. English.
The microformats wiki re-uses the W3C Manual of Style Spelling Editorial Guideline and thus uses U.S. English for page names, and contents of English-language pages, although British-English spellings MUST be preserved if originally used in:
- proper nouns
- direct quotations
- transcribed audio, where the speaker is known to use British-English
- user pages
You can help to implement this policy.