OK, after I removed fonts-droid package and installed those testing packages and configurations which using "Droid Sans Fallback" instead of "Droid Sans" today, everything seems to be good. Below are my testing results,
LANG=zh_TW.UTF-8 fc-match -s "Droid Sans" | head -n 10 DroidSansFallbackFull.ttf: "Droid Sans Fallback" "Regular" uming.ttc: "AR PL UMing TW" "Light" uming.ttc: "AR PL UMing HK" "Light" ukai.ttc: "AR PL UKai TW" "Book" DejaVuSans.ttf: "DejaVu Sans" "Book" DejaVuSans-Bold.ttf: "DejaVu Sans" "Bold" Waree.ttf: "Waree" "Book" ukai.ttc: "AR PL UKai CN" "Book" uming.ttc: "AR PL UMing CN" "Light" KhmerOS.ttf: "Khmer OS" "Regular"
LANG=zh_TW.UTF-8 fc-match -s "sans-serif" | head -n 10 DroidSansFallbackFull.ttf: "Droid Sans Fallback" "Regular" uming.ttc: "AR PL UMing TW" "Light" uming.ttc: "AR PL UMing HK" "Light" ukai.ttc: "AR PL UKai TW" "Book" DejaVuSans.ttf: "DejaVu Sans" "Book" DejaVuSans-Bold.ttf: "DejaVu Sans" "Bold" Waree.ttf: "Waree" "Book" ukai.ttc: "AR PL UKai CN" "Book" uming.ttc: "AR PL UMing CN" "Light" KhmerOS.ttf: "Khmer OS" "Regular"
LANG=zh_TW.UTF-8 fc-match -s "Droid Sans Fallback" | head -n 10 DroidSansFallbackFull.ttf: "Droid Sans Fallback" "Regular" uming.ttc: "AR PL UMing TW" "Light" uming.ttc: "AR PL UMing HK" "Light" ukai.ttc: "AR PL UKai TW" "Book" DejaVuSans.ttf: "DejaVu Sans" "Book" DejaVuSans-Bold.ttf: "DejaVu Sans" "Bold" Waree.ttf: "Waree" "Book" ukai.ttc: "AR PL UKai CN" "Book" uming.ttc: "AR PL UMing CN" "Light" KhmerOS.ttf: "Khmer OS" "Regular"
OK, after I removed fonts-droid package and installed those testing packages and configurations which using "Droid Sans Fallback" instead of "Droid Sans" today, everything seems to be good. Below are my testing results,
LANG=zh_TW.UTF-8 fc-match -s "Droid Sans" | head -n 10 ckFull. ttf: "Droid Sans Fallback" "Regular" Bold.ttf: "DejaVu Sans" "Bold"
DroidSansFallba
uming.ttc: "AR PL UMing TW" "Light"
uming.ttc: "AR PL UMing HK" "Light"
ukai.ttc: "AR PL UKai TW" "Book"
DejaVuSans.ttf: "DejaVu Sans" "Book"
DejaVuSans-
Waree.ttf: "Waree" "Book"
ukai.ttc: "AR PL UKai CN" "Book"
uming.ttc: "AR PL UMing CN" "Light"
KhmerOS.ttf: "Khmer OS" "Regular"
LANG=zh_TW.UTF-8 fc-match -s "sans-serif" | head -n 10 ckFull. ttf: "Droid Sans Fallback" "Regular" Bold.ttf: "DejaVu Sans" "Bold"
DroidSansFallba
uming.ttc: "AR PL UMing TW" "Light"
uming.ttc: "AR PL UMing HK" "Light"
ukai.ttc: "AR PL UKai TW" "Book"
DejaVuSans.ttf: "DejaVu Sans" "Book"
DejaVuSans-
Waree.ttf: "Waree" "Book"
ukai.ttc: "AR PL UKai CN" "Book"
uming.ttc: "AR PL UMing CN" "Light"
KhmerOS.ttf: "Khmer OS" "Regular"
LANG=zh_TW.UTF-8 fc-match -s "Droid Sans Fallback" | head -n 10 ckFull. ttf: "Droid Sans Fallback" "Regular" Bold.ttf: "DejaVu Sans" "Bold"
DroidSansFallba
uming.ttc: "AR PL UMing TW" "Light"
uming.ttc: "AR PL UMing HK" "Light"
ukai.ttc: "AR PL UKai TW" "Book"
DejaVuSans.ttf: "DejaVu Sans" "Book"
DejaVuSans-
Waree.ttf: "Waree" "Book"
ukai.ttc: "AR PL UKai CN" "Book"
uming.ttc: "AR PL UMing CN" "Light"
KhmerOS.ttf: "Khmer OS" "Regular"