Haha, yes, it's fair when English subtitles write something like [speaks Japanese], especially when at least one of the characters is not supposed to understand what's being said (when they do, it's more appropriate to write "[in Japanese]: let's go shopping!").

Netflix sometimes takes the cake with what I consider the most outrageous option: writing "[in English]" when they mean "in whatever language the protagonist considers native", which is mind-bogglingly wrong and hilarious at the same time.

They do this with the English subtitles of the German production "Die Kaiserin" ("The Empress"): whenever Sisi is speaking in another language, say French, the subtitles will say "[in French] I love you...", and when she switches back to German they will say "[in English] I love you...". WTF, Netflix? Note this is unrelated to understanding German; it's mostly Netflix looking down on its customers and assuming they cannot comprehend there are people in the world for whom their native tongue is different to the viewer's native tongue.

This has happened in more shows, enough to know it's not a fluke, though Netflix is inconsistent about it.