var conversion = new Conversion();
string latin = "a,b,v,g,d,đ,e,ž,z,i,j,k,l,m,n,o,p,r,s,t,ć,u,f,h,c,č,š,Lj,Nj,Dž,lj,nj,dž"; 
var cyrillicExtension = latin.ToSerbianCyrilic(); //Convert with extension method
var cyrillic = conversion.SerbianLatinToCyrillic(latin); //Convert with forwarded string
var latinConvert = conversion.SerbianCyrillicToLatin(cyrillic);
var latinExtension = cyrillic.ToSerbianLatin();