[Sync EN] variables: Describe how non-ASCII variable names behave instead of asserting they are unsupported (#5831)

[github-actions]

Commit: https://github.com/php/doc-en/commit/0e72b54621406de1c5642334258462725ca99a29
PR: https://github.com/php/doc-en/pull/5831

Archivos ES a actualizar

• language/variables.xml