This is what's in the file:
<languageList>
<Language>
<NameEnglish>System</NameEnglish>
<Name>System</Name>
<Id></Id>
</Language>
<Language>
<NameEnglish>English</NameEnglish>
<Name>English</Name>
<Id>1033</Id>
</Language>
</LanguageList>
Edit the file with a simple text editor like notepad(.exe)
The languages.xml is located in the folder /lang just below the BoincTasks.exe
These languages are displayed in Extra->Settings->General->Language.
To add an additional language, add the following:
<Language>
<NameEnglish>Dutch</NameEnglish>
<Name>Nederlands</Name>
<Id>1043</Id>
</Language>
The language name is displayed in the dropdown list as Nederlands (Dutch).
The id number can be found in Help->Show Log as:
User: 1043 (NLD), System: 1043 (NLD), Used: 1033 (ENU)
User: User selected language.
System: The OS installed language.
Use: The actually selected language.
The language selection sequence is:
1) The selected language.
2) The User language.
3) The System language.
4) The Fallback language 1033 (ENU) = English.
The initial selection is the first item in the list. In this case System = no language selected use User, System or Fallback.
Make sure you use the latest Beta version with the latest text.