plot hole in The Hitchhiker's Guide to the Galaxy - how does Marvin understand without a Babel fish?

He doesn't have ears, so no place to put a translating Babel Fish. He claims to have a "brain the size of a planet", so maybe that somehow enables him to understand everyone he meets. 

In a similar way, it was never explained how the Vogons were able to broadcast to Earth in English. 

Some relevant visual aids and the full version of the theme song:

Babel Fish - The Oddest Thing In The Universe - The Hitchhiker's Guide To The Galaxy - BBC

Marvin Vs The Tank

Journey of the Sorcerer (2013 Remaster)

The whole original series is available online, though I had to dig around to find the version I remembered (it was the 1990 cassette version). I should have bookmarked it, because I've been unable to relocate it. It's enough to make a guy shout "Belgium!"

Don't panic. Share and enjoy!