i18n phases 1+2: BAL translation layer and translatable texts

Phase 1: new bal/i18n.py, BAL's own gettext layer (domain "bal", catalogs
read with plugin.read_file()). _() asks Electrum's catalog first, then
BAL's, then returns the English source. The Qt plugin loads the catalog of
Electrum's GUI language at start-up; the CLI stays English.

Phase 2: every user-visible GUI text is now a whole, extractable sentence
(Ruff INT rules enabled). Class-level texts are marked with N_() and
translated when shown. Stored data stays language-neutral: the status
history is written in English and translated for display, the calendar
defaults follow the GUI language, and the history label and wallet labels
are never translated because BAL uses them to recognise its transactions.

No visible change apart from the double colon fixed in the will detail.
See CHANGELOG entries 58 and 59 and PLAN_I18N.md.

bal/gui/qt/common.py

@@ -52,7 +52,6 @@ from electrum.gui.qt.util import (
     read_QPixmap_from_bytes,
     webopen,
 )
-from electrum.i18n import _
 from electrum.logging import get_logger
 from electrum.network import BestEffortRequestFailed, Network, TxBroadcastError
 from electrum.payment_identifier import PaymentIdentifier
@@ -137,6 +136,7 @@ from ...core.will import (
     WillExpiredException,
     WillItem,
     WillPostponedException,
+    format_status_history,
 )
 from ...core.willexecutors import (  # noqa: F401
     Willexecutors,
@@ -144,6 +144,9 @@ from ...core.willexecutors import (  # noqa: F401
     is_tor_active,
 )
 
+# BAL's translator: Electrum's catalog first, then BAL's (see bal/i18n.py).
+from ...i18n import N_, _
+
 # --- Presentation helpers ---
 from .theme import (
     server_status_text,
@@ -161,6 +164,17 @@ from .window_utils import (
 
 _logger = get_logger(__name__)
 
+# Labels of bal.core.qrtransfer.CHUNK_PRESETS, marked for translation here
+# because qrtransfer.py must stay free of Electrum imports (the Android reader
+# ships a copy of it). The combos show them with _(label);
+# tests/test_i18n.py checks that this list matches CHUNK_PRESETS.
+QR_PRESET_LABELS = (
+    N_("Small - ~150 bytes/QR (low-res cameras)"),
+    N_("Medium - ~400 bytes/QR"),
+    N_("Large - ~900 bytes/QR"),
+    N_("XL - ~1800 bytes/QR (high-res cameras)"),
+)
+
 
 class shown_cv:  # noqa: N801  (intentionally lowercase: mirrors Qt signal naming)
     _type = bool
@@ -178,13 +192,30 @@ class shown_cv:  # noqa: N801  (intentionally lowercase: mirrors Qt signal namin
 
 
 def add_widget(grid, label, widget, row, help_):
-    grid.addWidget(QLabel(_(label)), row, 0)
+    """Add a ``label | widget | help button`` row to ``grid``.
+
+    ``label`` and ``help_`` must already be translated by the caller: a
+    variable passed to _() cannot be extracted into the catalog.
+    """
+    grid.addWidget(QLabel(label), row, 0)
     grid.addWidget(widget, row, 1)
     grid.addWidget(HelpButton(help_), row, 2)
 
 
 
 
+def translated_headers(headers):
+    """Return a translated copy of a list's ``headers`` class attribute.
+
+    The column headers are class attributes marked with N_(): a class body
+    runs at import time, before the catalog is loaded, so they are
+    translated here, each time the headers are (re)built.
+    """
+    return {column: _(text) for column, text in headers.items()}
+
+
+
+
 def log_error(exec_info, window=None):
     """Log an error and optionally show it.
 
@@ -222,7 +253,7 @@ def export_meta_gui(electrum_window, title, exporter):
     filter_ = "All files (*)"
     filename = getSaveFileName(
         parent=electrum_window,
-        title=_("Select file to save your {}".format(title)),
+        title=_("Select file to save your {}").format(title),
         filename="BALplugin_{}_{}_{}".format(
             BalPlugin.chainname, str(electrum_window.wallet), title
         ),
@@ -237,7 +268,7 @@ def export_meta_gui(electrum_window, title, exporter):
         electrum_window.show_critical(str(e))
     else:
         electrum_window.show_message(
-            _("Your {0} were exported to '{1}'".format(title, str(filename)))
+            _("Your {0} were exported to '{1}'").format(title, str(filename))
         )