Use flatten translation keys (#36225)

Crowdin does not remove empty lines in nested JSON translation files.
Therefore, we use flattened translation keys instead. We have also
updated the key-loading logic to ensure that empty values are not
applied during translation.

---------

Signed-off-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: TheFox0x7 <thefox0x7@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>

build/update-locales.sh

@@ -9,11 +9,11 @@ fi
 mv ./options/locale/locale_en-US.json ./options/
 
 # Remove translation under 25% of en_us
-baselines=$(wc -l "./options/locale_en-US.json" | cut -d" " -f1)
+baselines=$(cat "./options/locale_en-US.json" | wc -l)
 baselines=$((baselines / 4))
 for filename in ./options/locale/*.json; do
-  lines=$(wc -l "$filename" | cut -d" " -f1)
-  if [ $lines -lt $baselines ]; then
+  lines=$(cat "$filename" | wc -l)
+  if [ "$lines" -lt "$baselines" ]; then
     echo "Removing $filename: $lines/$baselines"
     rm "$filename"
   fi