You can speculate as much as you like... It simply cannot be shown wIth any degree of certainty that it was not a translation error
But it can, it is clearly indicated in GM's statements in words which cannot possibly be a translation error. There is only one door that can be locked and unlocked from the outside and that is the front door leading to the car park. Similarly, there is only one sliding door into the lounge and that is the rear patio door.
G McCann Police Statement 11.15am on 4th May 2007"As usual, every half hour and as the restaurant was near, the witness or his wife, would check whether the children were all right. In this way, at about 21.05 the witness came to the Club, entered the room using his respective key, the door being locked, went to his children's bedroom and checked that the twins were fine, as was Madeleine. "He then went to the WC" where he remained for a few moments, left..."
https://www.mccannpjfiles.co.uk/PJ/GERRY-MCCANN.htmG McCann Police Statement 3.20pm on 10th May 2007"Despite what he said in his previous statements, he states now and with certainty, that he left with KATE by the rear door which he consequently closed but did not lock given that that is only possible from the inside. Referring to the front door, while he is certain that it was closed it is unlikely that it was locked as [because] they had left by the rear door."
"At 21H05 MATHEW returned, the time at which the deponent left the table to go to check how his children were.
----- He followed the normal route up to the rear door, which being open he only had to move [slide] it, that being the way in which he entered [was entering] the lounge..."
https://www.mccannpjfiles.co.uk/P4/04_VOLUME_IVa_Page_891.jpgSomehow I don't think one can blame an interpreter/translator for those words.