use embed.fs wrapper for langFS so lang/ is not needed in paths

[files]lang_files is now the path to the lang directory, not path to a
directory containing it.

config/config-base.json

@@ -867,7 +867,7 @@
                     "requires_restart": true,
                     "type": "text",
                     "value": "",
-                    "description": "The path to a directory CONTAINING a 'lang/' directory, which follow the same form as the internal one. See GitHub for more info."
+                    "description": "The path to a directory which following the same form as the internal 'lang/' directory. See GitHub for more info."
                 }
             }
         }

embed.py

@@ -13,18 +13,30 @@ with open("embed.go", "w") as f:
     if EMBED in trues:
         f.write("""package main
 import (
-    "embed"
+	"embed"
-    "log"
+	"io/fs"
+	"log"
 )
 
 //go:embed data data/html data/web data/web/css data/web/js
 var localFS embed.FS
 
 //go:embed lang/common lang/admin lang/email lang/form lang/setup
-var langFS embed.FS
+var lFS embed.FS
+
+var langFS LangFS
+
+type LangFS struct {
+	fs embed.FS
+}
+
+func (l LangFS) Open(name string) (fs.File, error)          { return l.fs.Open("lang/" + name) }
+func (l LangFS) ReadDir(name string) ([]fs.DirEntry, error) { return l.fs.ReadDir("lang/" + name) }
+func (l LangFS) ReadFile(name string) ([]byte, error)       { return l.fs.ReadFile("lang/" + name) }
 
 func loadLocalFS() {
-    log.Println("Using internal storage")
+	langFS = LangFS{lFS}
+	log.Println("Using internal storage")
 }""")
     elif EMBED in falses:
         f.write("""package main
@@ -42,5 +54,5 @@ func loadLocalFS() {
     log.Println("Using external storage")
     executable, _ := os.Executable()
     localFS = os.DirFS(filepath.Dir(executable))
-    langFS = os.DirFS(filepath.Join(filepath.Dir(executable), "data"))
+    langFS = os.DirFS(filepath.Join(filepath.Dir(executable), "data", "lang"))
 }""")

main.go

@@ -339,10 +339,10 @@ func start(asDaemon, firstCall bool) {
 		}()
 	}
 
-	app.storage.lang.CommonPath = "lang/common"
+	app.storage.lang.CommonPath = "common"
-	app.storage.lang.FormPath = "lang/form"
+	app.storage.lang.FormPath = "form"
-	app.storage.lang.AdminPath = "lang/admin"
+	app.storage.lang.AdminPath = "admin"
-	app.storage.lang.EmailPath = "lang/email"
+	app.storage.lang.EmailPath = "email"
 	externalLang := app.config.Section("files").Key("lang_files").MustString("")
 	var err error
 	if externalLang == "" {
@@ -577,7 +577,7 @@ func start(asDaemon, firstCall bool) {
 	} else {
 		debugMode = false
 		address = "0.0.0.0:8056"
-		app.storage.lang.SetupPath = "lang/setup"
+		app.storage.lang.SetupPath = "setup"
 		err := app.storage.loadLangSetup(langFS)
 		if err != nil {
 			app.info.Fatalf("Failed to load language files: %+v\n", err)