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

modules/translation/i18n/localestore.go

@@ -131,16 +131,15 @@ func (l *locale) TrString(trKey string, trArgs ...any) string {
 	var format string
 	idx, ok := l.store.trKeyToIdxMap[trKey]
 	if ok {
-		if msg, ok := l.idxToMsgMap[idx]; ok {
-			format = msg // use the found translation
-		} else if def, ok := l.store.localeMap[l.store.defaultLang]; ok {
+		format = l.idxToMsgMap[idx]
+		if format == "" { // missing translation in this locale, fallback to default
+			if def, ok := l.store.localeMap[l.store.defaultLang]; ok {
 				// try to use default locale's translation
-			if msg, ok := def.idxToMsgMap[idx]; ok {
-				format = msg
+				format = def.idxToMsgMap[idx]
 			}
 		}
 	}
-	if format == "" {
+	if format == "" { // still missing, use the key itself
 		format = html.EscapeString(trKey)
 	}
 	msg, err := Format(format, trArgs...)