My proposed discussion forum would be dedicated to any and all instances in movies in which language and/or information pertaining to language/linguistics is incorrect. For example, here are two examples that have been bugging me forever, hence my desire to start a discussion forum.

Return of the Jedi (1983) - C3PO refers to the Ewoks as speaking 'a very primitive dialect'. There's no such thing as a 'primitive' language. If one variety is less complex, say phonologically or morphologically, than another, it will often make up for this in other ways, as well as the fact that there are legitimate reasons for its relative lack of complexity when compared with other varieties of the language. It has nothing to do with speaker intelligence. I think Lucas was perhaps making the point that a band of 'primitive' Ewoks were nonetheless able to help defeat the almighty Galactic Empire, but the reference to their language as being primitive is simply incorrect from a linguistic point of view. The fact C3PO referred to their language as a dialect per se, might also reinforce the negativity attached to their speech, in that public perception is sometimes still of the opinion that dialects are somehow 'wrong', simply as they are non-standard forms. We know this is not true.

Likewise, Princess Leia, disguised as a bounty hunter at the start of the film, uses a language in which much is communicated using the same repetitive phrase of 'yoto' for the most part. Not a mistake per se, but a unique language indeed to communicate so much with so little!

The Living Daylights (1987) - In this 007 film, James Bond refers to his love interest, Kara, with the word ښايسته [Kha-yessta]. However, he identifies the language as Afghan - there is no such language as Afghan! Surely, someone who is as knowledgeable as our James would know this! The language in question is Pashto.

Signs (2002) - The character of Merrill, played by Joaquin Phoenix, shouts at the TV screen for a group of Brazilian children to move out of the way, using the imperative vámonos, meaning 'let's go'. However, this is Brazil and so the children would be speaking Portuguese, not Spanish. However, this was probably a deliberate mistake on the part of the writer, M. Night Shyamalan, to portray Merrill as a bit lacking in general knowledge (plus he was very excited when he shouted at the TV screen, given that an alien was on the streets in this Brazilian town).

Linguistic Field(s): Applied Linguistics
Discipline of Linguistics
General Linguistics