Google's John Mueller said on Twitter that going capital or lower case does not matter much when it comes to setting the country-region code in your XML sitemap files.
He said either "en-US" OR "en-us" are perfectly fine to use.
This comes after one webmaster said he was getting an "unknown language code(sitemap)" error. John did add that "one tricky one I've seen is either normal spaces or unicode no-width spaces accidentally used in a sitemap file."
But generally, the letter case does not matter here.
Here are the tweets:
Both are fine. One tricky one I've seen is either normal spaces or unicode no-width spaces accidentally used in a sitemap file.
— John ☆.o(≧▽≦)o.☆ (@JohnMu) July 29, 2017
Forum discussion at Twitter.
