Naming of movies and search by filename

No, Plex won’t do that by default.
It will only do that in 2 cases:

  1. your file has embedded meta tags which contain the original title and you have told Plex to “prefer embedded metadata”
  2. you have told Plex to use the original title in the properties of your movie library

In all other cases, after identifying (“matching”) the movie Plex will try to find the localized title of the movie, depending on the “language” setting of your movie library.

I think that’s a good idea and it could help in quite a few various cases.
However, you have already posted this as a feature suggestion: Search by filename