Final answer:
The language is determined by the locale settings of the operating system when there is no default language system property set, often established based on the user's location and preferences during OS installation.
Step-by-step explanation:
If no default language system property is set on a computer, the language is typically determined by the locale settings of the operating system. The locale settings dictate the language used for system-level services and applications. These settings are often established during the installation of the operating system based on the user's location and preferences. If the user does not explicitly set a language preference, the system will usually default to a language that is determined by the regional settings of the installed operating system version.