That looks not like a 2-pole lowpass filter, but like a Butterworth filter.
However it illustrates good the coding overhead of MQL4, even though it's also based on C. A 3rd order Butterworth filter in lite-C looks like this:
var Butterworth(var *Data,int Cutoff)
{
var a = exp(-PI / Cutoff);
var b = 2*a*cos(1.738*PI / Cutoff);
var c = a*a;
var c1 = b + c;
var c2 = -(c + b*c);
var c3 = c*c;
var c0 = 1 - c1 - c2 - c3;
var* Filt = series(*Data,4);
return Filt[0] = c0*Data[0] + c1*Filt[1] + c2*Filt[2] + c3*Filt[3];
}