If an interface or application cannot handle a user's language, then you don't have any interface at all.
Internationalization is an underlying part of an application's infrastructure and architecture.
It must be approached with the same level of planning and market concern as you would in choosing between a command-line approach or GUI as an interface for end users. Localizable All messages, icons, and human-readable content must be externalized and easily translated. The translated message, or resource, files must be seamlessly loadable by the application, depending on the current language and locale settings for the session, data-item, data stream, or user. The application must correctly handle all character data based on the attributes of the character data, not the encoding. Ideally, an application or installation should operate independently of the underlying operating system's default character encoding.