Thank you very much for your help. The solution you provided does exactly what I want.
The following is raw code snippet that does the trick, if anybody else is interested.
declare @name nvarchar(50)
declare @description nvarchar(500)
declare @id int
set @name = 'name'
set @description = 'description'
insert into UserGroup default values
set @id = SCOPE_IDENTITY()
insert into UserGroupTranslation select @id, Language.LanguageID, @name, @description from Language