There is a clear difference between spoken and written Japanese. The written Japanese is very neutral – contains no respectful, humble and/or patronizing languages, and is also gender neutral. This makes written Japanese markedly unnatural when used as spoken language and vice versa. So much so that it is very difficult to write good lyrics for rock music in Japanese. In English you can mix literary sentences and colloquial sentences pretty seamlessly, but in Japanese the gap is too wide that it will sound weird.
However “spoken language” in Japanese is not necessarily “informal” language. There are plenty of very polite, respectful words that are usually used only while speaking.
- 閉店時間は八時で御座います -> Our closing time is 8PM (very polite, but only in spoken language)
- 閉店時間は八時です -> Our closing time is 8PM (in written language. very neutral)