Over and over I find myself thinking about each line of the great Wagner texts that we are working on 'Aha! this line is the key, the heart of the drama!' then the same thought for the line that follows, then the next... This continuum of intense revelation, with no pause except between acts, combined with the time-scale of the unfolding, starts to suggest a style required for the titling text to make that unfolding available to the English-speaking attendee. There might be a balance (also likely the wrong word) to achieve in searching for the English, between packing each line with maximum impact and significance, and quite the opposite: draining the line of all distraction, the burden of 'thought' for the audience member, so that it can be registered and dismissed in a flash, without inviting any comparison or internal debate: all eyes and engagement right back to the stage.
Here's a test case to play with: the times when Tristan and Isolde say each others' names to one another
Act I scene 5 once, as they discover and express the love that they have, then upwards of four times, singing over one another in wild passion, more or less in public; Act II scene 2 (once); Act III (once, as Tristan dies.)
So, as Wagner wrote, and the characters sing:
....what should we see on the screen? Put yourself there in the theatre as a spectator, what would you see that best allows trouble-free engagement with the stage?