Which 2nd language to learn? Java or .NET

I am a software developer in my mid-40s. Have been programming the same language all these time (shame on me, desktop development only in Delphi), only know little about HTML, CSS. Have 1.5 year in CSharp desktop progamming. Always thinking of I need an insurance and also in dev world a second language is important. First of all to choose either desktop development or go to web development field. Then to choose second programming language.

Can you comment on these and tell me the reason of your choice? Thanks.