Hello all, this is my first time posting. Nice to meet you all!
I have been reading and following this forum since the Winter Olympics, I watched it here and there, but a certain answer from our Winter Prince regarding which Olympic performance he remembers the most (it's Nathan's!) piqued my curiosity to know him more, so I watched his programs and fell in love, and livestreamed the World Championships for the first time to watch him fight for the Japan's three spots (a crash course on why World Championships are important and how the spots are given were done here :sad4

with all his heart and, well, basically, surrendered to the fact that I will probably love him for the rest of my life
I have to say this query is quite interesting:
Answering in native language is fine. Understanding the question is my point.
Most obvious was when Shoma kept turning back to the male translator(his manager?) at WC 2018 small medal ceremony. Cos whenever a question is asked immediately Shoma will turn back look at the male translator for the translation. Sometimes with a puzzled look.
While Kolyada looked like he understood the question and gave his answer to the translator.
Its not as hilarious as Yuzuru at WC 2012 nodding at the question and then right after that going to Takahashi for the translation. Still obvious.
Some of my country's athletes do that, a question asked in English, they straight away answer in native tongue. The translator translates the answer. It's to speed things up.
2nd, when Shoma was asked what Yuzuru & Javier were saying during the bro hug and tears part at OG 2018 - Shoma said he didnt know, they were talking in English.
All this lead me to believe Shoma understands very little English, much less speak it. And yes, I have met many people who dont understand English.
So, in short how do I know? From his facial expression and action. Of course, Shoma may understand more than he's letting on.
I think as a skater, Shoma does understand English words and phrases related to skating and daily greetings. But it's not enough to follow/carry a long conversation, and more importantly, answering questions from the press which tends to be more complicated than greetings. Also, he seems to be the type of person who lose concentration when the question/conversation is long and not in his native language and wasn't started by him, so I think turning to the translator/his manager is his way to make sure that he gets the questions right and the answers he give is properly given too.
If we listen to his (very short!) conversation with Stephane, it's basically this:
Shoma: "Stephane!" (Stephane's first name, of course, they have known each other at least since Shoma first turn senior?)
Shoma: "Twizzles..." (Twizzles is a transition element and used commonly in choreo, Shoma's worked with Stephane before and his choreo included twizzles so this should be a familiar word for him)
Shoma: "How many? One.. two.." and immediately followed by Shoma physically doing the twizzles. This was the tip to me, because if Shoma is confident that Stephane understand his English he would stop at "How many?", there is no need to do the twizzles. But he did, because I think he wants to make sure that Stephane understands and he's not sure just by saying the question is enough.
Also, I noticed Shoma finally said "Ok!" after Stephane physically confirms "One, two, three.. out!" which, again, shows that he still needs the reassurance by physical demonstration, not just the conversation itself. It must be noted that this is a conversation that Shoma himself initiated, so he knows what he's asking and the answer he is seeking from Stephane, which is different from press conferences.
Another tip is Arriba's lovely memory from Chicago when he answers "Thank you too," to the thanks said to him ahahah! It's very sweet but if Shoma understands English more it should probably be a "You're welcome".
I think Shoma's grasp of English reminds me of my own in Japanese. I can understand some words and can say some useful phrases to navigate when I'm traveling there, but the moment I was addressed to have a conversation in the language.. I blanked out and can only smile nervously! I remember the small medal ceremony in Milan which I think you were referring too when his manager (not the usual translator he has in press conferences) was also on stage to translate, you can see that Shoma keeps looking at him because the MC was very active and gesturing to him a lot, and of course the lively crowd was waiting for his answers. It's a different setting from press conferences which are more formal. I do think he understands English words and phrases (another fan on Twitter recalls that he knows the phrase "I have to go", which comes very handy if he is ushered by officials from fans), but in situations like that I think he was just making sure that he answers all questions properly.
So, I do agree that he may understand more than he lets on (probably not the Yuzu-Javi Olympics conversation because it was all very fast and Yuzu was half-crying and Shoma looks half-asleep ahahah), but in Shoma style he would rather make sure that he understand all questions in a language he understands the most, making sure that all answers are properly given.
I notice Shoma doesn't talk a lot, every answer he gives shows how much thought he gives into it.