Summary:
Now that Structured Data On Commons (a.k.a. "Captions" or "WikibaseMediaInfo") are deployed, it would be nice to submit something from the app also to structured data.
Steps to reproduce:
Post an image with all fields filled. Check the result. Currently it posts nothing to the WikibaseMediaInfo captions.
Commons app version:
2.9.0.164
Is this issue about the same thing as #2096? :-)
Yeah, closely related. Can be closed as duplicate if you want.
I'd say that captions are more for descriptions than filenames, but the general idea is that the app should submit _something_ directly to the captions and not just to the template.
This should be pretty easy from the App.
All you need is one or many calls to the wbsetlabel API module on commons.
The parameters should be pretty straight forward, the entity ID that you will need to use is the media info entity ID. This is currently the pageid prefixed with an M, so for a page with pageid = 77, the mediainfo ID would be M77. This assumption is likely to never change.
Captions are a bit like a title, but multilingual, and limited to 255 characters. More at https://www.mediawiki.org/wiki/Help:File_captions
The underlying idea is that filenames are risky to modify (all links break at each typo correction) and they are not translatable, so when showing a picture the software would show this caption under it, rather than the filename (which might be in Swahili) or the description (which might be a huge wall of text).
I suggest we just:
A description is a collection of peculiar details, some of whom might be of interest to a fraction of the readers. Thus I think a description does not make a good caption in the sense of a string of text to put under an image.
Take this example:

https://commons.wikimedia.org/wiki/File:R%C3%A9union_publique_de_La_R%C3%A9publique_En_Marche_!_Japon,_avec_le_d%C3%A9put%C3%A9_C%C3%A9dric_Villani_le_jeudi_26_novembre_de_%C3%A0_Akasaka,_Tokyo.jpg
Step 1:

Step 2:

To be honest, I don't have a strong opinion, as long as _something_ useful is submitted. The Commons Android app can be an excellent source for submitting to Structured Data. Perhaps the designers and the PMs of Structured Data have a more educated opinion? I'll invite them to this discussion.
Can I work on this improvement ?
I read about the issue and what I understood is caption, which is short most relevant information about the picture, is to be included along with description, which is detailed information about the picture.
The work on the app is:
Is that right ? or Is there something I misunderstood ?
@amire80 @nicolas-raoul
@abhishekd08 Yes, it is yours :-)
Yes, you are right. Please refer to my UI mocks at https://github.com/commons-app/apps-android-commons/issues/2297#issuecomment-453988747 . Please also remove the "Title" field in the first screen. The first caption is used as a filename.
Thanks!
1. add UI to include captions in multiple languages
There should probably be a default field for a caption in the language in which the app is being used, and a reasonably easy way to add more captions in other languages.
@amire80 Yes, exactly like what is done currently for descriptions :-)
I am getting this gradle sync error. I tried but cannot understand the problem, can anyone tell how to solve this it please ?
Can anyone please tell how to solve the build error ?
We must get the user's approval that caption are licensed CC0 (independently from the image's license).
Here is how the upload wizard does that: https://commons.wikimedia.org/wiki/Commons_talk:Structured_data#CC0_licensing_mockups

Assigned to @vanshikaarora (GSoC 2019). Anyone interested in collaborating on this task or offering tips, don't hesitate to post here :-)
I just released a new version of WikidataToolkit that supports MediaInfo editing. It should also work on Android if it helps. I have also made two examples, one for retrieval and one for edit.
Thanks @Tpt ! :)
Below is the structured-data branch right now.
Things to fix in the UI:

Closing this, issues created for each of the two remaining problems.
Most helpful comment
I just released a new version of WikidataToolkit that supports MediaInfo editing. It should also work on Android if it helps. I have also made two examples, one for retrieval and one for edit.