Japanese Mathematics Vocabulary: "We don't use this word."

I had an interesting experience several weeks ago. I recently finished my Masters Degree in Education specializing in English Language Learner Education and I am now adapting my teaching practice to help my English Language Learners. 

I realized that there was a lot of mathematics vocabulary that I didn't know in Japanese and I was limited when I was explaining something to my Japanese speaking students. So I contacted my friend who is a mathematics teacher at Kanagawa Sogo High School and has very good English. I went thought my Geometry textbook and wrote down most of the vocabulary words and a few others that I felt I would want to know in order to explain Geometry to my students in Japanese. I had somewhere around 250 words.

When we sat down and began going through the words, my friend kept saying "_________ is the word for that, but we don't use this word." I would guess that somewhere around one third of the vocabulary words that I brought, they don't use in their K-12 education. Perhaps some of this is the difference in curriculum. However my friend said that they would simply describe the word. For example we teach the word "colinear" but in Japanese schools they would simply describe the points as being on the same line or draw a picture. The same thing with coplanar, skew lines, exterior angles. and the list goes on. There isn't even a word in Japanese for a linear pair, they simply call them supplementary angles or explain that because they make a straight line, their measures would add to 180 degrees.

I walked away from our meeting wondering why we have so many vocabulary words in Geometry and mathematics in general. Because I will be teaching a Mathematics Lab next year with students from Algebra as well, I asked about some Algebra words. I again found that words like "leading coefficient" and others were not used in Japanese K-12 education. We teach students vocabulary words for concepts that we study for only one or two days. I think part of the reason is the way we were taught, so there is a culture of education that focuses on vocabulary words. 

I think Japanese education is correct when they limit the vocabulary words that they teach to the most important words that will be used throughout the course, not for a few days. Limiting the number of vocabulary words would make the mathematics more accessible to all students. However, I am afraid to do this in my practice because if I do not expose them to these words, then I will be hurting my advanced students when they go to future math classes and their teacher is using a word that I thought was unnecessary. The change has to happen in the curriculum, starting with the textbooks.