Youmu's canonical language is all over the place:
Humble and formal among the people she respects.
Sometimes a bit rude among friends and foes.
And once in a while also a bit childish.
But one aspect that stands out:
Contrary to popular belief she uses a lot of female language, be it interjections like "ara" and "maa" or particles like "wa", "kashira" and "nano".
Even the Japanese fandom completely ignores the latter aspect. I don't know of a single doujinshi that had her use any of those feminine terms.
A few even mentioned it in the foreword or afterword and yet the artists still decided that it seems too out of character.
But considering that Yuyuko was the only woman around Youmu for most of her life, it shouldn't even be that surprising.
It's also an aspect that's completely lost in the translation.