How to change the language of the Symphony Interface?

In Lotus Symphony 1.2 and later versions

Click File -> Preferences -> IBM Lotus Symphony -> Regional Settings
You need to change the language used in the User Interface of IBM Lotus Symphony.

NOTE: The language of user interface in Regional Settings applies to text used in Symphony menus and dialog boxes only.  
For date format, time format and currency, you may use different locale.

Restart Lotus Symphony for changes to take effect in the product's user interface.

In Lotus Symphony 1.0 and 1.1

For versions prior to Lotus Symphony 1.2, there is no preference setting for selecting a language of the user interface.  
To change the language used in the User Interface of IBM Lotus Symphony on these versions:
Edit the application shortcut used to launch Symphony using a text editor

Add the parameter -nl followed by the desired language.

Example:  In order to start Symphony using the US English locale, the shortcut on Windows could resemble the following:  

"C:\Program Files\IBM\Lotus\Symphony\symphony.exe" -nl EN_US

Known Limitations:

• English locale: This function will not work if Symphony is installed on computers with locale in English .
• Font support: The operation system should support the font for the new UI language after changing, otherwise characters might be rendered and displaying incorrectly.
• Language Package: Language package will not automatically install. Hence, if the user does not install the NLV package manually, the documentation in the product help files and tips will continue to appear in English.
  Once language package is installed, long tips, help content and template will also change after switched to new language.

To download and install additional languages, read: Downloading and installing language dictionaries in Lotus Symphony