English description of mode parameter says: "The mode of the conversion. It can be one of MB_CASE_UPPER, MB_CASE_LOWER, MB_CASE_TITLE, MB_CASE_FOLD, MB_CASE_UPPER_SIMPLE, MB_CASE_LOWER_SIMPLE, MB_CASE_TITLE_SIMPLE, MB_CASE_FOLD_SIMPLE. "
Spanish description of mode parameter says: "El modo de conversión. Puede ser MB_CASE_UPPER, MB_CASE_LOWER, o MB_CASE_TITLE."
Maybe translation is missing some of available constants.
Regards.
From manual page: https://php.net/function.mb-convert-case
English description of mode parameter says: "The mode of the conversion. It can be one of MB_CASE_UPPER, MB_CASE_LOWER, MB_CASE_TITLE, MB_CASE_FOLD, MB_CASE_UPPER_SIMPLE, MB_CASE_LOWER_SIMPLE, MB_CASE_TITLE_SIMPLE, MB_CASE_FOLD_SIMPLE. "
Spanish description of mode parameter says: "El modo de conversión. Puede ser MB_CASE_UPPER, MB_CASE_LOWER, o MB_CASE_TITLE." Maybe translation is missing some of available constants. Regards.