When the film is in a language you don't read
Subtitlezz is a free browser app that plays a subtitle file on your phone in time with a film on a screen you do not control. It is for anyone sitting in front of a film in the wrong language: dubbed, undubbed, or subtitled into a language they cannot read.
Three versions of the same problem
The film is dubbed. Much of continental Europe dubs everything by default. If you have moved to Spain, Italy, Germany or France and your target language is not there yet, the local multiplex is closed to you for anything but the rare original-version showing.
The film is in its original language with no subtitles at all. Common for English-language films screened in English-speaking countries, which is fine until the film is in Korean for twenty minutes, or the accent is one you cannot follow.
The subtitles are there, in the wrong language. A Berlin cinema showing a Japanese film with German subtitles serves everyone in the room except the Italian speaker. This is the case nobody plans for, and the one that comes up constantly if you live abroad.
What you do instead
Bring the subtitle file you actually need and play it yourself. Search for
one in the app or load your own .srt or .vtt, press
play on the first line of dialogue, and read from your lap while the film
runs.
Nothing on the cinema's side has to change, and nothing about the screening has to be special. Which showing you attend stops being a constraint.
Getting the right file for a dubbed screening
This is the one thing worth care. Match the file to the runtime of the cut being screened, not just the title. A subtitle timed against a 142 minute cut drifts steadily against a 138 minute one, and nudging cannot close a gap that keeps growing.
Dubbed releases sometimes run to a slightly different cut than the original, so if a file drifts steadily rather than sitting at a fixed offset, the file is wrong and no amount of adjusting will fix it. Find another.
It does not translate anything
Subtitlezz plays a file you supply. It does not listen to the film, transcribe it, or translate it live. There is no microphone and no machine translation, because a live translation of dialogue you cannot verify is a confident guess, and a confident wrong subtitle is worse than no subtitle.
The translation work has already been done by whoever wrote the subtitle file. This is the thing that plays it at the right moment.