refactor(es_extended): backfill locale from English once at load

Instead of checking the English fallback on every Translate call, fill the missing keys into the target locale the first time it loads, log the gaps, and drop the English table. The active locale ends up self-contained: no per-call fallback and only one table stays in memory.

[core]/es_extended/locale.lua

@@ -11,14 +11,48 @@ local function localeFallbackEnabled()
     return GetConvar("esx:localeFallback", "true") ~= "false"
 end
 
---- Lazily load and cache a locale file, false if it cannot be read
+--- Read and execute a locale file, returning its table or false if unreadable.
+local function readLocale(locale)
+    local success, result = pcall(function()
+        return assert(load(LoadResourceFile(GetCurrentResourceName(), ("locales/%s.lua"):format(locale))))()
+    end)
+
+    return success and result or false
+end
+
+--- Copy every key the target locale is missing from English into it once, warn
+--- about the gaps, then let the English table go. The locale ends up
+--- self-contained, so no per-call fallback and only one table stays in memory.
+local function backfillFromEnglish(locale, translations)
+    local english = readLocale("en")
+    if not english then
+        return
+    end
+
+    local missing = {}
+    for key, value in pairs(english) do
+        if translations[key] == nil then
+            translations[key] = value
+            missing[#missing + 1] = key
+        end
+    end
+
+    if #missing > 0 then
+        print(("[es_extended] locale [%s] is missing %d translation(s), falling back to English: %s")
+            :format(locale, #missing, table.concat(missing, ", ")))
+    end
+end
+
+--- Lazily load and cache a locale file, false if it cannot be read.
 local function loadLocale(locale)
     if Locales[locale] == nil then
-        local success, result = pcall(function()
-            return assert(load(LoadResourceFile(GetCurrentResourceName(), ("locales/%s.lua"):format(locale))))()
-        end)
+        local translations = readLocale(locale)
 
-        Locales[locale] = success and result or false
+        if translations and locale ~= "en" and localeFallbackEnabled() then
+            backfillFromEnglish(locale, translations)
+        end
+
+        Locales[locale] = translations
     end
 
     return Locales[locale]
@@ -44,15 +78,6 @@ function Translate(str, ...) -- Translate string
         return translations[str]:format(...)
     end
 
-    -- The locale exists but is missing this key: borrow the English string
-    -- rather than surfacing a placeholder.
-    if Config.Locale ~= "en" and localeFallbackEnabled() then
-        local english = loadLocale("en")
-        if english and english[str] then
-            return english[str]:format(...)
-        end
-    end
-
     return ("Translation [%s][%s] does not exist"):format(Config.Locale, str)
 end
 
@@ -62,4 +87,4 @@ end
 
 _ = Translate
 -- luacheck: ignore _U
-_U = TranslateCap
+_U = TranslateCap