'Declaration
 
Public Sub Add( _
   ByVal LCID As Integer _
) 

public void Add( 
   int LCID
)

public:
void Add( 
   int LCID
) 

Parameters

LCID

LCID (Locale ID) of the language to be added. The locale ID passed with the first call will be considered as the base language. The LCID is used as "Dictionary Key" for the corresponding dictionaries (see example in Localization of Project Files in Designer). The elements of the base language also correspond to the UsedIdentifiers (see also LlGetUsedIdentifiers) that are written to the project files.

The following shows how the three languages German, English, and French are registered as design languages in Designer.

...
// Define LCIDs int designerLanguageLCIDde = new CultureInfo("de").LCID;
int designerLanguageLCIDen = new CultureInfo("en").LCID;
int designerLanguageLCIDfr = new CultureInfo("fr").LCID;
               
// Add/declare the available design languages in the Designer
// according to their respective LCID
LL.DesignerWorkspace.DesignerLanguages.Add(designerLanguageLCIDde);
LL.DesignerWorkspace.DesignerLanguages.Add(designerLanguageLCIDen);
LL.DesignerWorkspace.DesignerLanguages.Add(designerLanguageLCIDfr);
...

Platforms: Windows 10 (Version 21H2 - 22H2), Windows 11 (22H2 - 25H2), Windows Server 2016 - 2025
.NET: .NET Framework 4.8, .NET 8, .NET 9, .NET 10

Reference

DesignerLanguages Class
DesignerLanguages Members