Using one xeCJK font family on English and Chinese at the same time

Question

I've tried to use font family to change the font of text that consist of Chinese characters and English alphabets. But it seems to only affect Chinese characters.

Is there any way I can change the font of them using the same font family?

\documentclass{standalone}
\usepackage{xeCJK}

\newCJKfontfamily\familyA{NotoSansCJKtc-Medium}
\newCJKfontfamily\familyB{NotoSansCJKtc-Light}
\newCJKfontfamily\familyC{NotoSansCJKtc-Regular}
\newCJKfontfamily\familyD{NotoSansCJKtc-Black}

\begin{document}
{   \familyA 中文 Eng     } ||
{   \familyB 中文 Eng     } ||
{   \familyC 中文 Eng     } ||
{   \familyD 中文 Eng     } 
\end{document}{}

Answer 1

You should take the concept of a "font family" serious, i.e. instead of using different families for different weights, you should use a single family with suitable font commands to switch between font weights. In addition, you should define a corresponding font for Latin characters. Here I am using Noto Serif:

\documentclass{standalone}
\usepackage{fontspec}
\setmainfont{NotoSerif}[
  UprightFont=*-Regular,
  BoldFont=*-Bold,
  FontFace={l}{n}{*-Light},
  FontFace={mb}{n}{*-Medium},
  FontFace={k}{n}{*-Black},
]


\usepackage{xeCJK}
\setCJKmainfont{NotoSansCJKtc}[
  UprightFont=*-Regular,
  BoldFont=*-Bold,
  FontFace={l}{n}{*-Light},
  FontFace={mb}{n}{*-Medium},
  FontFace={k}{n}{*-Black},
]

\DeclareRobustCommand\lseries{\fontseries{l}\selectfont}
\DeclareTextFontCommand{\textl}{\lseries}
\DeclareRobustCommand\mbseries{\fontseries{mb}\selectfont}
\DeclareTextFontCommand{\textmb}{\mbseries}
\DeclareRobustCommand\kseries{\fontseries{k}\selectfont}
\DeclareTextFontCommand{\textk}{\kseries}

\begin{document}
{   \mbseries 中文 Eng     } ||
{   \lseries 中文 Eng     } ||
{   中文 Eng     } ||
{   \kseries 中文 Eng     }

\end{document}

Result:

Note that this answer is partially based on https://tex.stackexchange.com/a/264275/140850.