Matroska, commonly identified by the MKV extension, is a container that can hold multiple media tracks and associated information. A file can include several audio languages or subtitle tracks, but their presence is not guaranteed. Playback requires the player to understand both the container and the particular formats used inside it.
A practical example
A film file may offer two audio tracks and several subtitle tracks through a compatible player's controls. Another MKV file may contain only one audio track, so the same menu cannot manufacture a language that was never included in the file.
A common misunderstanding
A container's capacity for extra tracks does not establish what a particular file contains. Inspect the available tracks rather than assuming a filename or extension promises a language selection.
Related terms
Further reading
Stable technical definition. Editorial approach