Page header set does not work with sites in a different language. Line 289 of is referring to 'Site Pages' this does not work if your lcid is not 1033 https://github.com/pnp/office365-cli/blob/33c9780a8664ef0c0a4595ea5ab7db0de8f9e3b0/src/o365/spo/commands/page/page-header-set.ts

url: ${args.options.webUrl}/_api/web/lists/getByTitle('Site Pages')/items(${pageItemId})