Anime characters are almost always drawn with... "anime" facial features. Eyes are big and round, every color is allowed for eyes and hair (not to mention hairstyle), etc.
Since there are anime series starring both Japanese and non-Japanese characters, how can one distinguish them? I'm asking both in-universe and out-of-universe.
Comments and answers to this question claim that Western characters tend to be drawn with big noses, square jaws, blond hair, wide mouth, etc. But to me it seems not always the case! For example, in Yu-Gi-Oh, Bandit Keith has some of these features, but Pegasus Crawford has not, and they are both supposed to be American. Naruto, Jonouchi etc are blond and Japanese. Most characters in Escaflowne have a long nose regardless of their origin.
For even more blatant examples, let's compare Lelouch Lamperouge and Suzaku Kururugi from Code Geass:
or Teletha "Tessa" Testarossa and Kaname Chidori from Full Metal Panic:
Same big round eyes. Same pointy chin. Very similar noses. And, for the two girls, crazy hair color. (Similar comparsions can be done for Light Yagami an L from Death Note, and for many others).
I'd say that, at least out-of-universe, the viewer is expected to tell them apart only from their names (or, in case of biracial characters, from the double surname, e.g. Asuka Langley-Sohryu, Kallen Stadtfeld-Kozuki) and from dialogue (e.g. a character declare his/her origin). But I wonder: am I missing something? Are there subtle physical traits that the viewer is supposed to use to get their origin before they declare it?
Theoretically, there shouln't be the need to tell them apart: a character (like a real person) is defined by his/her actions, not from his/her ethnicity. But in-universe, characters seem to always recognize at a glance if another character is Japanese or not. For example, in an episode of Full Metal Panic, Sosuke asks to free first the Japanese girl (Kaname), then the Western one (Tessa), as it is obvious to everyone who is who. In Code Geass, the distinction beween Britannians and Japanese is an important plot point, and people doesn't seem to need to know the name of a character to tell if he/she is Britannian or Japanese.
So is there some kind of artistic convention? A physical equivalent to a translation convention? E.g. when we audience know that Suzaku is Japanese and Lelouch isn't, should we assume that in-universe they HAVE different facial traits? (or, in the case of Kallen: after she says that she is half-Britannian half-Japanese, are we supposed to imagine her with some "mix" of features so that other characters can identify her as both Britannian and Japanese?)