How does the Tardis translation system work in Doctor Who?

But over the years the translation circuit has been referenced and explained in various different ways. The first mention came in 1976 episode The Masque of Mandragora, when Tom Baker’s Fourth Doctor described the translation to companion Sarah-Jane Smith (Elisabeth Sladen) as a “gift of the Time Lord” that he allowed her to share.

In more recent years, however, it’s been retconned as a circuit closely linked to both the Tardis's telepathic field and the Doctor, with Rose Tyler (Billie Piper) no longer able to understand alien languages when the Doctor was recovering from his regeneration in 2005’s The Christmas Invasion.

But it’s never been clear exactly how the circuit works. Over the years some dialogue has remained untranslated (for example when the Second Doctor meets German and French soldiers in The War Games or the Tenth Doctor met Judoon police in 2008) as well as plenty of signs and posters, though in 2011 episode A Good Man Goes to War it was suggested there was a “lag” in the system when it came to the written word.

There have also been some languages that the Tardis doesn’t translate, including an old Aborigine dialect in Fifth Doctor story Four to Doomsday, a complex alien language in 1980’s The Leisure Hive and incredibly ancient languages like the words of the Minotaur in 2012’s The God Complex and the language of the Beast in 2006’s The Impossible Planet. Judoonese, by contrast, is apparently too simplistic to be translated, which could also be the explanation behind why the speech of some more bestial aliens – as well as human infants and real-life animals – is left unclear to the audience.

The Doctor himself has been shown to be able to bypass the system to speak words in different languages (for example the Tenth Doctor’s catchphrase of Allons-y, the French for ‘let’s go’) due to his superior control over the system, while normal users have a slightly different response. For example, when Donna Noble (Catherine Tate) tried to speak Latin while the Tardis was translating her words into that language, it was filtered back into her own tongue which was perceived as Celtic by the Romans.

Elsewhere, it’s also a little unclear exactly who the translation applies to in any given scene. In the same Christmas episode mentioned above, when the Doctor wakes up (see video below) Rose, the Sycorax invaders and the Earth government are all suddenly able to understand each other despite the Doctor not being aware of the situation or even who is standing outside his Tardis, suggesting the translation is a rather passive process and not dictated by who’s actually been in the Tardis or been “given” the ability by the Doctor.

This week’s episode The Eaters of Light muddies the waters even further, with Roman soldiers and native Picts discovering that they can now understand and speak each other’s languages thanks to the presence of the Doctor, despite never having been part of the Tardis’ telepathic field and not being anywhere near it at the time of the discovery.

So what’s the answer for all these inconsistencies and confusing moments? Well, one could be that this is a conceit for a children’s television programme that we should be taking less seriously, but an in-universe explanation often suggested by fans is that the Doctor’s old, out-of-date and battered Tardis has a slightly faulty translation system, occasionally not functioning or functioning sporadically depending on the situation and the complexity of the language it’s faced with.

It has also been suggested that the Doctor has an affinity for language beyond the translation field itself, which could explain why he’s able to communicate so easily with babies and horses while his companions (and by extension, the viewers) are unable to understand those particular languages.

For our part, we’d like to think the inconsistency is a little like the reasoning behind the Tardis’s faulty targeting system, which flings the Doctor all over space and time based on where the time machine thinks he needs to be rather than where he necessarily wants to be. Maybe in this week's episode the Tardis thought a little communication could save the day, and perhaps at other times it sees the value of keeping other languages unclear – even if it is just to make the Doctor’s adventures that bit more challenging and dramatic.

Doctor Who continues on BBC1 next Saturday 24th June at 6:45pm