All parts of OS X and many applications of third-party vendors are multi-lingual. This means the user interface of an application can be switched between different languages without having to install special language-specific versions of the program. Under normal circumstances, the language that will be used by an application is determined when launching it. OS X checks the available language support packages embedded in the application and compares it to the user’s priority list of preferred languages. The first language in the list which matches a language package available in the application will “win” and will be chosen to become the active language for running the program. Each user can modify her personal priority list at System Preferences > Language & Region > Preferred languages. You can add all languages you like to use with the [+] below the language table, and the drag the languages into your preferred order of priority. The first language in the table will become you primary language.
TinkerTool System allows you to temporarily ignore your personal language priority list, forcing an application to launch in a specific language, different from your usual preferred one. Neither your language preferences, nor the language packages within the application will be touched. This can be very helpful if you are working in a multi-lingual country or organization. This is also helpful to give remote support to a user which has configured his OS X setup for a language different from yours. You can even run the same application multiple times, using different languages in each instance.
Some applications might not be prepared to run concurrently in the same user session. Conflicts can arise when the multiple instances modify the same configuration files, so you should be careful when changing data. Please check the documentation of the applications for possible information.
Perform the following steps to launch an application in a specific language:
If the application you are launching does not provide support for the language you have selected, the application’s standard language will be chosen. This is usually the language the application was originally developed for.