i18n: bake the .lang files into boards that cannot rely on the Store (V4)

gen-lang-builtin.py generates src/ui-touch/i18n_builtin.h from the SAME
deploy/apps/lang/*.lang files the Store serves, so the downloaded and the
compiled-in translations can never drift — translators still edit one place.
TR() consults the loaded file overlay first, then the baked table, then
English, so a downloaded language still wins on boards that can fetch one.

CAP_BUILTIN_LANGS is ON for the V4 (its net worker is fragile at ~95%
internal RAM, so the Store is not dependable there and it would otherwise be
stuck on English) and OFF elsewhere. Cost is FLASH only, no RAM:
  V4     71.7% -> 85.5%
  T-Deck 75.5% (unchanged, gate off)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

scripts/build/gen-lang-builtin.py

@@ -0,0 +1,112 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+"""Bake deploy/apps/lang/*.lang into a compiled-in fallback table.
+
+Boards that can reach the Lua Store download their language as a file. Boards
+that cannot (the V4: ~14 KB of free internal heap, so the net worker and the
+store are unreliable there) still need translations, and before this they were
+stuck on English.
+
+This generates src/ui-touch/i18n_builtin.h from the SAME .lang files the store
+serves, so the two can never drift: translators edit deploy/apps/lang/*.lang,
+and both paths follow. Rows are emitted sorted by key so TR() can binary-search
+them, and the table lives in .rodata — flash, not RAM.
+
+Run from the repo root (a PlatformIO pre-build step does this automatically):
+    python3 scripts/build/gen-lang-builtin.py
+"""
+import glob, os, sys
+
+ROOT = os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+LANGDIR = os.path.join(ROOT, 'deploy/apps/lang')
+OUT = os.path.join(ROOT, 'src/ui-touch/i18n_builtin.h')
+
+# Index order must match the UiLang enum in i18n.h.
+CODES = ["en", "hu", "nl", "de", "fr", "es", "it",
+         "ru", "uk", "bg", "sr", "el", "pt-br", "ro"]
+
+
+def c_escape(s):
+    out = []
+    for ch in s:
+        if ch == '\\':   out.append('\\\\')
+        elif ch == '"':  out.append('\\"')
+        elif ch == '\n': out.append('\\n')
+        elif ch == '\t': out.append('\\t')
+        elif ch == '\r': out.append('\\r')
+        elif ord(ch) < 0x20: out.append('\\x%02x' % ord(ch))
+        else: out.append(ch)
+    return ''.join(out)
+
+
+def read_lang(path):
+    """key -> value, with the file's own \\n/\\t/\\\\ escapes decoded."""
+    rows = {}
+    for line in open(path, encoding='utf-8'):
+        line = line.rstrip('\n').rstrip('\r')
+        if '\t' not in line:          # header/comment lines carry no tab
+            continue
+        k, v = line.split('\t', 1)
+        def un(t):
+            o, i = [], 0
+            while i < len(t):
+                if t[i] == '\\' and i + 1 < len(t):
+                    n = t[i + 1]
+                    o.append('\n' if n == 'n' else '\t' if n == 't' else n)
+                    i += 2
+                else:
+                    o.append(t[i]); i += 1
+            return ''.join(o)
+        k, v = un(k), un(v)
+        if k and v:
+            rows[k] = v
+    return rows
+
+
+def main():
+    langs = {}
+    for code in CODES[1:]:                      # English is the key itself
+        p = os.path.join(LANGDIR, code + '.lang')
+        if os.path.exists(p):
+            langs[code] = read_lang(p)
+
+    if not langs:
+        sys.exit('no .lang files found in ' + LANGDIR)
+
+    w = ['// Generated by scripts/build/gen-lang-builtin.py — DO NOT EDIT.',
+         '// Source: deploy/apps/lang/*.lang (the same files the Lua Store serves).',
+         '// Compiled-in fallback for boards that cannot rely on downloading a language.',
+         '#pragma once', '#include "i18n.h"', '']
+
+    for code in CODES[1:]:
+        rows = langs.get(code, {})
+        sym = 'kBuiltin_' + code.replace('-', '_')
+        w.append('static const I18nPair %s[] = {' % sym)
+        for k in sorted(rows):                  # sorted: TR() binary-searches
+            w.append('  { "%s", "%s" },' % (c_escape(k), c_escape(rows[k])))
+        w.append('};')
+
+    w.append('')
+    w.append('static const I18nPair* const kBuiltinLang[LANG_COUNT] = {')
+    w.append('  nullptr,')                       # LANG_EN: the key is the English
+    for code in CODES[1:]:
+        sym = 'kBuiltin_' + code.replace('-', '_')
+        w.append('  %s,' % (sym if langs.get(code) else 'nullptr'))
+    w.append('};')
+    w.append('static const int kBuiltinLangCount[LANG_COUNT] = {')
+    w.append('  0,')
+    for code in CODES[1:]:
+        sym = 'kBuiltin_' + code.replace('-', '_')
+        w.append('  %s,' % (('(int)(sizeof(%s)/sizeof(%s[0]))' % (sym, sym))
+                            if langs.get(code) else '0'))
+    w.append('};')
+    w.append('')
+
+    open(OUT, 'w', encoding='utf-8').write('\n'.join(w))
+    total = sum(len(r) for r in langs.values())
+    print('%s: %d languages, %d rows, %d bytes' %
+          (os.path.relpath(OUT, ROOT), len(langs), total, os.path.getsize(OUT)))
+
+
+if __name__ == '__main__':
+    main()

src/ui-touch/device_caps.h

@@ -263,3 +263,16 @@
 #ifndef CAP_LUA_APPS
   #define CAP_LUA_APPS 1
 #endif
+
+// Compile the translations into the image (i18n_builtin.h, generated from
+// deploy/apps/lang/*.lang) instead of relying on downloading a .lang file.
+// ON for boards where the Lua Store is not dependable — the V4 runs at ~95%
+// internal RAM with Wi-Fi up, so its net worker and the store are fragile and
+// it would otherwise be stuck on English. Costs ~400 KB of FLASH, no RAM.
+#ifndef CAP_BUILTIN_LANGS
+  #if defined(HELTEC_LORA_V4_TFT) || defined(HELTEC_LORA_V4)
+    #define CAP_BUILTIN_LANGS 1
+  #else
+    #define CAP_BUILTIN_LANGS 0
+  #endif
+#endif

src/ui-touch/i18n.cpp

@@ -1,5 +1,9 @@
 #include "i18n.h"
 #include <string.h>
+#include "device_caps.h"
+#if CAP_BUILTIN_LANGS
+#include "i18n_builtin.h"   // generated: baked-in translations
+#endif
 
 // Native language names shown in the picker. Index order == UiLang.
 const char* const kUiLangNames[LANG_COUNT] = {
@@ -38,7 +42,11 @@ bool i18nHasFileOverlay() { return s_file_n > 0; }
 
 const char* TR(const char* en) {
   if (!en) return "";
+#if CAP_BUILTIN_LANGS
+  if (!s_file_n && s_ui_lang == LANG_EN) return en;
+#else
   if (!s_file_n) return en;   // no language file loaded: the keys ARE the English UI
+#endif
   // Icon-prefixed labels ("<glyph>  Copy") carry the LVGL symbol's UTF-8 bytes
   // (3-byte private-use sequences, 0xEE/0xEF lead) in the lookup key, but the
   // table is keyed on the plain text — so those labels never matched and the
@@ -62,6 +70,18 @@ const char* TR(const char* en) {
       if (c < 0) hi = mid - 1; else lo = mid + 1;
     }
   }
+#if CAP_BUILTIN_LANGS
+  if (!v && s_ui_lang != LANG_EN && kBuiltinLang[s_ui_lang]) {
+    const I18nPair* tab = kBuiltinLang[s_ui_lang];
+    int lo = 0, hi = kBuiltinLangCount[s_ui_lang] - 1;
+    while (lo <= hi) {                     // sorted by the generator
+      const int mid = (lo + hi) / 2;
+      const int c = strcmp(base, tab[mid].key);
+      if (c == 0) { v = tab[mid].val; break; }
+      if (c < 0) hi = mid - 1; else lo = mid + 1;
+    }
+  }
+#endif
   if (!v) return en;                       // untranslated: original, prefix intact
   if (plen == 0) return v;                 // plain key: the table cell directly
   static char ring[4][120];