Currently some messages such as videojs-quality and videojs-more-information can be translated via translatewiki. Other translations that live in TimedMediaHandler's resources folder are copied from upstream repo. This makes things confusing and difficult for translators.
I think all needed messages could be made translatable via translatewiki. This might be similar to how Leaflet messages are handled within Kartographer extension. Or, alternatively, if current approach is really desirable, then this should be documented in mediawiki.org for translators.