Feature summary (what you would like to be able to do and where):

It would be great if functionality was added to detect the language of the file-title (when one has entered text into the title input box and then left the focus/clicked on another input box) as already done on other sites where language detection seems to work fairly quickly. It would not need to detect the language and just check whether the title is English. I strongly oppose facilitating and encouraging non-English titles that would degrade understandably/accessibility and usefulness of Commons by letting the user specify the language without language detection.

Then, if it detected the title is not English, it would show a box asking the user to specify the language, similar to the language box for file captions on Wikidata.

By the way, if it detected gibberish / some undescriptive IDs or numbers like Fig1345643, it could also display a info/warning note that the file title should be useful/descriptive.

The upload should not be made more complicated and time-intensive/laborious so I suggest that for an upload of multiple files at once all non-English titles are automatically detected and the input-box for the titles-language is shown at the top where the user needs to specify it just once (in just a second or so as it has autocomplete) and it's then set for all the files detected and marked as having non-English titles in the files the user is uploading.

That filename language could be set via structured data and/or the linked categories.

Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):

Having the file-title language specified could for example aid in or facilitate the creation of captions (e.g. at least for those files that are used in English Wikipedia or some other Wikipedia not of the same language as the title representing broader relevance).

In categories like Category:Microscopic images relating to biology the image itself isn't always (even usually) self-explanatory so if I can't read the title, I don't know what that file shows. One idea for the future – and it could be decades from now – would be to display the caption of the file in your language instead or above the original file title if 1. the title is not in your language and 2. a file caption in your language exists. There may also be other ways this could be addressed for better accessibility / understandability / localization / usefulness.

Created a bot task request to set categories of Category:Files by language of non-English file title at the Commons bot work requests page here.

For future uploads, it would be best if this was addressed at the time of upload, at the source.

Benefits (why should this be implemented?):

The earlier this is done, the easier it would be to at some point have quite complete and reliable metadata about filetitle language which again could be used to make Commons more multilingual in the sense of better understandable to Commons and Websearch users across the world. See use-cases for further and more info on benefits.