English is the primary language for this film.

@scgary66​ 

I see no style guide that suggests that "in" should be capitalized. In fact, IMDb rules says it should (so no wonder it wasn't accepted):

English language words which must begin with a lower-case letter (unless at the end of a title) are: a an and as at by for from in of on or the to with

The real correction here is that it should be "The Spy That Came in from the Cold". "From" should not be capitalized. (Edit: This is why linking is better. I see you just mistyped the title and "from" is not capitalized.)

Well, the list of non-capitalized words in the style guide consists entirely of articles, prepositions and conjunctions, in keeping with standard grammatical rules; I suspect IMDb wrote it that way to keep it simple, and not rely on contributors to distinguish parts of speech. It's unfortunate, but I hope we're not stuck with it; perhaps the guide could be tweaked a bit by stating the reason for non-capitalization, noting the parts of speech with examples. Here's an outline of the major style guides on the topic, all of which indicate to capitalize adverbs (though there's some conflict on the issue of short words): Title Capitalization Tool - Capitalize My Title - Title Case Tool.

Anyway, the language issue seems to be fixed.

P.S. The same issue applies to titles including Get on Up and Get on the Bus.