Nihon or Nippon
From my experiences of teaching Japanese, there are many people who don’t know a Japanese word for Japan and those wh know the word often think Japan is Nippon. In my daily life, I use only nihon. Nihongo o hanasu (speak Japanese), nihon ni sundeiru (live in Japan), nihonshu o nomu (drink Japanese sake) etc. I rarely use Nippon. However, Nippon is often used for especially a name of comapnies, schools or other organizations.
An example for Nippon that I can think of is “gambare Nippon”, which people would say when they support their favorite national sports team. Nihon has a soft impression and Nippon has a strong one. That’s why Nippon is often used in sports.
Can you find the difference? “Ho” is soft. On the other hand, you make a sound “po” with a little of strength, don’t you? I think this difference is the origin of onomatopoeia which is one of the chracteristic of Japanese.
An impression of “ha” line (ha, hi, hu, he and ho) is soft and has a feeling that strength is falling out.
“Pa” line (pa, pi, pu, pe and po) has a light and popping impression.
One of the popular onomatopoeia is “perapera”.
Kare no nihongo wa perapera desu. (His Japanese is fluent.)
Just as fluency in speaking foreing lanugage is described with “perapera”, it has a feeling that you are stepping up the tempo of action.
As you see, each line has a characteristic of sounds. Especially ka line, sa line, ga line and za line are easy to get its characteristic. Ka line has a light and hard impression and sa line has a refreshing one. On the other hand, ゛(tenten) makese ga and za lines rough and unpleasant.
Also, I think that this type of sound impressions is globally shared to some extent. It is not something only Japanese can feel. For instance, an English word “pop” has the same impression as pa line I mentioned before and means “make a short sharp explosive sound or cause to burst with such a sound.” Moreover, “crisp” (kurisupu) has ku and su, so it has a light sound which is the same as “karikari” and “sakusaku”. They decribe crisp texture when you bite food.
Do you know any other examples like these in your language?