Isn't the whole "speaks foreign language" subtitle thing due to the show itself not subtitling said foreign language? As in (and I hope I don't come off the wrong way), nine times out of ten it reflects the language barrier in the show itself amongst the characters.
The problem with putting "[Speaks foreign language]" isn't about it hurting the Vibes of the show, it's about the inherent inequality it causes between hearing and hoh/deaf viewers.
If someone is watching a show in English with Spanish as a language used periodically, a hearing viewer who speaks both English and Spanish will be able to understand everything being said, while a deaf viewer who reads/speaks both English and Spanish is refused subtitles for a possibly significant portion of the show.
I think, perhaps, the reason your thought process is so common among people in my notes is that people are conflating subtitling with translation. If a language barrier is a part of the story-telling (a poor, alienating decision in show writing, almost always), then the words don't need to be translated, but they should still be subtitled.
A translation, in shows where foreign languages should be understood, is usually built into the show, as many hearing viewers watch without subtitles on. However, when captions/subtitles are turned on, every spoken word should be subtitled in the language it's spoken in.
