XLL add-ins built with XLL+ offer support for languages other than English.
The error messages returned by XLL+ can be delivered in a selected language, or in the language of the current Excel user. For example, the following error message:
#ERROR: Expected at least 1 value for X
can appear in French:
#ERREUR: Au moins 1 valeur attendue pour X
See Error messages for more information about selecting a language for error messages.
Help files can be generated in the language of your choice. See Help: Languages other than English for more information.
The standard function categories of the Excel Formula Wizard, such as "Database", "Information" and "Date & Time" will appear in the language of the user or of the Excel version being used.