@jhadred
Anko is a food item, and it's very common to not translate names for food items unless there's already an English name for them.
All the other words you listed are not translatable in short form. Senpai = senior? Kind of but not really. It doesn't convey the strict hierarchy and rigid social structure it implies in Japan. It also misses the fact that age is not necessarily the controlling factor. A senpai can be younger than you in some situations.
The problem with making a super short translator note like "seiso = pure" is that that accomplishes none of the expected goals of translator notes. Am I supposed to think that seiso exactly means pure with almost perfect matching? That's the feeling I get there. I honestly don't know if that's true, but the translator note is what makes me believe that. After a quick search, I get the feeling it's supposed to be closer to "refreshing", which matches with the picture in the panel, but the translator note leaves that out.
There are only two options here. 1) The translator note is inaccurate because it doesn't actually explain what seiso means, or 2) the translator note is completely unneeded because they could've just written pure.