Is there a way to search for a word across all metadata fields? As far as I can see search is limited to the selected metadata “field”, so it is either tag or title or description etc. I’d like to search all of them if possible, which would be typical for a disorganised person like myself 
If it can not be done in dt, XnView MP has a search option All Fields and just now found a count of 64 contains “en” on my HD, starting at ‘Desktop’ and recursing all sub-folders.
Is the text search in the collections filter module, as described in a recent post, sort of what you want? It can be pinned to the top tool bar if you use it a lot.
This works as narrowing down the search, so if “test” is not in the Title but it is in Description, it will not show. Unless I am doing something wrong.
Don’t select “Narrow down search” but “Add more images”
“Collection filters” → “search” might also work for you, but be aware, this module works “on top” of the “Collections” module.
See darktable user manual - collection filters section “text search”.