ClearAll[ImportAll]
ImportAll[lang_String] :=
 Module[{data, continue, cmcontinue, extra, xml, next},
  data = {};
  continue = True;
  cmcontinue = "";
  While[continue,
   extra = If[cmcontinue =!= "", "&cmcontinue=" <> cmcontinue, ""];
   xml = Import["http://www.rosettacode.org/w/api.php?action=query&list=categorymembers&cmtitle=Category:" <> lang <> "&cmlimit=500&format=xml" <> extra, "XML"];
   AppendTo[data, Cases[xml, XMLElement["cm", _, {}], \[Infinity]]];
   next = Flatten[Cases[xml, {"cmcontinue" -> _}, \[Infinity]]];
   If[Length[next] > 0,
    next = First[next];
    cmcontinue = "cmcontinue" /. next;
    ,
    continue = False;
    ];
   ];
  Cases[Flatten[data], HoldPattern["title" -> x_] :> x, \[Infinity]]
  ]
Complement[ImportAll["Programming_Tasks"], ImportAll["Mathematica"]]