Okay, that is a very good suggestion, but it's a different idea.
In these examples, both people speak their own languages, with English subtitles. Even if the viewer can't tell the difference between Old Norse and AngloSaxon (I'm guessing?), they can easily figure out which characters understand one another and which characters do not. And the audience is let in on the 'private' conversations via subtitles.
I think that is a common enough way to do it. I haven't watched that show, so I don't know if there are other scenes where these characters speak in English. I assume there are? And the audience just accepts that they're switching into Old Norse now because they are around people who don't understand them?
I ask, because this is commonly done with one language that is 'always' foreign.
Game of Thrones' Valerian, for example, is always spoken as itself, and characters switch to English when they stop speaking it. Same with the Grounders language in
The 100.
In this scene, everyone who is speaking English has a language in common. When they switch to subtitled 'Grounder' (a pidgin of English, essentially), that means they are speaking their own language. No one ever speaks English on screen while they are supposed to be speaking Grounder.
What we're requesting here is the opportunity to 'switch' into the languages if there are people present who might not understand. So, Sindar and Quenya both appear in a scene with speakers of both, and then it's all English if everyone present understands the language of the speaker. Right?
Our situation is that we've had both languages represented as English to this point, and will open the Season with the Noldor speaking English to one another.
So, I am fine with the very next scene being one where the Sindar approach the Camp of Fingolfin and speak Sindarin (with subtitles) and the Noldor answer them with Quenya (with subtitles), but that is a little different than the idea that the Sindar approach speaking English amongst themselves, and then are brought up short by the Noldor responding to them in Quenya. I'll make sure we suggest both variations to the Hosts.