Titles on classical releases should mostly follow the printed information, with any changes required by the language-specific classical guidelines. Note that many classical releases have a less detailed tracklist at the back and a more detailed one in the booklet. When choosing titles, it's generally better to follow the more detailed one, if available.
Extra work information
Do list key, catalog number, movement numbers, etc. if they are included as part of the titles on the release, but not otherwise; that information is already available at the work level, so it doesn't need to be forced into the track titles if the release doesn't include it. "Sonata no. 1: Allegro" is a perfectly acceptable track title, if that's what is on the release. Similarly, do not "complete" the information: if a release says "in G", there is no need to extend it to "in G major".
Full work title
For groups of tracks that are marked as part of a full work (with e.g. a header), add the full work title (as listed on the release) to all tracks from the work, separated with a colon.
As on cover:
And not only for the first track:
Do this even if the full work title is only on the release title (for example, in a release that contains only a full performance of the Goldberg Variations, the first track title should still be something like "Goldberg Variations: Aria", not just "Aria").
Similarly, for operas, oratorios, cantatas and other works divided in acts/parts, do mention the act or part on all tracks, not only the first track of each one.
If a track which is an extract of a larger work is listed on the release as "Part from Work" (e.g. "Allegro from Symphony no. 5") or as "Part title" (e.g. "Una furtiva lagrima") just enter it as-is, there's no need to turn it into "Work: Part".
When a release has titles in several languages (for example, English / German / French), enter the tracklist in the main language of the release. If all languages are given equal weight, just pick one. The others can be entered as pseudo-releases and linked to the release marked as official with the appropriate relationship.