translations: add note that f-strings cannot be translated

and replace current usage

electrum/gui/kivy/uix/screens.py

@@ -404,7 +404,7 @@ class SendScreen(CScreen):
                     self.app.wallet.delete_invoice(key)
                 self.update()
         n = len(invoices)
-        d = Question(_(f'Delete {n} invoices?'), callback)
+        d = Question(_('Delete {} invoices?').format(n), callback)
         d.open()
 
 
@@ -522,7 +522,7 @@ class ReceiveScreen(CScreen):
                     self.app.wallet.delete_request(key)
                 self.update()
         n = len(requests)
-        d = Question(_(f'Delete {n} requests?'), callback)
+        d = Question(_('Delete {} requests?').format(n), callback)
         d.open()
 
 

electrum/gui/qt/channels_list.py

@@ -108,7 +108,7 @@ class ChannelsList(MyTreeView):
         chan = self.lnworker.channels[channel_id]
         to_self_delay = chan.config[REMOTE].to_self_delay
         msg = _('Force-close channel?') + '\n\n'\
-              + _(f'Funds retrieved from this channel will not be available before {to_self_delay} blocks after forced closure.') + ' '\
+              + _('Funds retrieved from this channel will not be available before {} blocks after forced closure.').format(to_self_delay) + ' '\
               + _('After that delay, funds will be sent to an address derived from your wallet seed.') + '\n\n'\
               + _('In the meantime, channel funds will not be recoverable from your seed, and might be lost if you lose your wallet.') + ' '\
               + _('To prevent that, you should have a backup of this channel on another device.')

electrum/gui/qt/lightning_dialog.py

@@ -66,14 +66,14 @@ class LightningDialog(QDialog):
         self.set_unknown_channels('', len(self.network.lngossip.unknown_ids))
 
     def on_channel_db(self, event, num_nodes, num_channels, num_policies):
-        self.num_nodes.setText(_(f'{num_nodes} nodes'))
-        self.num_channels.setText(_(f'{num_channels} channels'))
+        self.num_nodes.setText(_('{} nodes').format(num_nodes))
+        self.num_channels.setText(_('{} channels').format(num_channels))
 
     def set_num_peers(self, event, num_peers):
-        self.num_peers.setText(_(f'Connected to {num_peers} peers'))
+        self.num_peers.setText(_('Connected to {} peers').format(num_peers))
 
     def set_unknown_channels(self, event, unknown):
-        self.status.setText(_(f'Requesting {unknown} channels...') if unknown else '')
+        self.status.setText(_('Requesting {} channels...').format(unknown) if unknown else '')
 
     def is_hidden(self):
         return self.isMinimized() or self.isHidden()

electrum/i18n.py

@@ -30,6 +30,9 @@ LOCALE_DIR = os.path.join(os.path.dirname(__file__), 'locale')
 language = gettext.translation('electrum', LOCALE_DIR, fallback=True)
 
 
+# note: f-strings cannot be translated! see https://stackoverflow.com/q/49797658
+#       So this does not work:   _(f"My name: {name}")
+#       instead use .format:     _("My name: {}").format(name)
 def _(x):
     global language
     return language.gettext(x)

electrum/lnworker.py

@@ -819,7 +819,7 @@ class LNWallet(LNWorker):
             if success:
                 break
         else:
-            reason = _(f'Failed after {attempts} attempts')
+            reason = _('Failed after {} attempts').format(attempts)
         self.network.trigger_callback('invoice_status', key)
         if success:
             self.network.trigger_callback('payment_succeeded', key)