I've never asked what first goes through their heads on the beginner level; but when they get the proper pronunciation, they pronounce the voiced "th" as "d" and the voiceless "th" as "t"... like my Tanks example.

In Turkish, all letters are pronounced (except for the g that has a mark over it - making the letter silent). So the town Fethiye is "fate - hee - yay". Quite often students will go back to pronouncing something as they would in Turkish, which gives the dilemma of "cigarettes" as "jiggarets" because the "c" is pronounced as "j".