In your case, the monospace font did not support Chinese characters, and therefore an (undesirable) fallback Chinese font is used that did not "cooperate" with your English letters in monospace font.
Also, you cannot change the glyph width of the font to any desired width using CSS though font-stretch exists. Adjusting size or width works, but it affects both Chinese and English text, and width are based on the width of spaces.
Unfortunately, there are no easy way. Your best bet is to use a font such that it is monospace, and that it supports Chinese characters, and that Chinese characters are twice as wide as English letters.