It is, but it is neither easy nor pretty. At least the solution that I came up with. It's quite possible there is a much more elegant way to do this, but this is what I got.
For this demo
I only worried about SRT subs (see below for to handle all filetypes), you will have to adjust for more filetypes, which is going to make this solution even uglier and more difficult (although there is probably a solution using regex).
All of the below assumes that you have your external subtitles saved alongside the movie file in the same folder.
First, you're going to want to want your external subs imported into MC. Here are directions on how to do so
https://yabb.jriver.com/interact/index.php/topic,87545.0.html. The linked thread is about importing comic books into MC, so adjust accordingly. I ended up adding this to my Custom Resources file “Subtitles (srt)” . You will need to restart MC a this point. Then import your subtitles. I would suggest starting with a single movie and if you find this works, go on from there.
You are going to need a few new fields. For this exercise, I have four scratch fields that I use for experimentation, they are [_a], [_b], [_c] and [_d] (this keeps them at the top of the list for easy access) you will probably want to rename them to something logical.
For [_a] I have a value of
if(isequal([Media Sub Type], Movie, 1), RemoveRight([Filename],3)srt,)
What this does is take the movies filename, remove the last three letters, which is the files extension and replace it with srt. So Movie_title_1999.mkv becomes Movie_title_1999.srt
For [_b] I have a value of
if(isequal([filename], srt, 8), [filename],)
This is just saying if the filename contains srt, then print the filename otherwise don't print anything.
For [_c] I have a value of
if(isequal([Media Type], Data, 1), [_b],[_a])
So, if your media type is equal to data, which your subtitles will be, then [_c] will display [_b] and if the media type is not equal to data then [_c] will display [_a]
Finally, for [_d] I have a value of
ItemCount(/[filename /(path/)/[_c/])
This uses the somewhat new ItemCount feature which counts items with the same value in a given field or set of fields.
If a movie has an srt file in the same folder as the movie, [_d] will display 2. If there is no external subtitle file, [_d] will display 1.
Then, in your tooltip you could have something like
if(isequal([_d], 2, 1), This movie has external subtitles,)
Some of the above could probably be condensed to fewer fields, but I like to break things into smaller chunks as I find it easier to work that way, YMMV.