fix: parse fee rate with the invariant culture

On Italian/German systems "1.5" was read as 15 sat/vB. The Send form,
the Donate form and the CLI now share CoinAmount.TryParseFeeRate
(invariant culture, '.' or ',' as decimal separator, range (0, 1000]).
Donate and the CLI report an invalid rate instead of silently using 1.

CHANGELOG.md

@@ -9,6 +9,11 @@ release and covers the full history from the initial commit.
 
 ### Fixed
 
+- Fee rate parsing no longer depends on the system culture: on Italian/German systems `1.5`
+  was read as `15` sat/vB (10x the intended fee). The Send form, the Donate form and the CLI
+  `--feerate` now share `CoinAmount.TryParseFeeRate` (invariant culture, `.` or `,` as decimal
+  separator, no thousands separators, range (0, 1000] sat/vB). Donate and the CLI no longer
+  silently fall back to 1 sat/vB on an invalid value: they report an error.
 - `ElectrumClient`: after a protocol error (e.g. a malformed line from the server) the read
   loop died but the client kept reporting `IsConnected == true`, and any later request waited
   forever for a response that could never arrive. The read loop now marks the connection dead

USERGUIDE.md

@@ -382,7 +382,8 @@ wallet must be spendable (not watch-only) to actually broadcast.
 - **Fee (sat/vB)** — a single manually-entered fee rate. **Default: 1 sat/vB.** There are no
   presets and no automatic fee estimation. On the Palladium chain, blocks are rarely full,
   so 1 sat/vB normally confirms in the next few blocks; raise it if a transaction lingers in
-  the mempool. Must be a number greater than zero.
+  the mempool. Must be a number greater than zero and at most 1000; `.` or `,` is the decimal
+  separator (no thousands separators), regardless of the system language.
 - **QR scan** (Android only) — camera button; reads a plain address or a
   `palladium:` payment URI (the address part is used).
 
@@ -439,7 +440,7 @@ software of your choice, then broadcast the finalized transaction.
 
 The Help overlay includes a donation form (developer address
 `plm1qdq3gu2zvg9lyr8gxd6yln4wavc5tlp8prmvfay`) using the same prepare/confirm flow and the
-fee rate from the Send tab (falling back to 1 sat/vB if invalid). Entirely optional.
+fee rate from the Send tab (an invalid rate is reported as an error). Entirely optional.
 
 ---
 

src/App/ViewModels/MainWindowViewModel.Donate.cs

@@ -44,9 +44,11 @@ public partial class MainWindowViewModel
                 DonatePreview = Loc.Tr("msg.amount.invalid");
                 return;
             }
-            if (!decimal.TryParse(SendFeeRate, System.Globalization.NumberStyles.Any,
-                    System.Globalization.CultureInfo.InvariantCulture, out var feeRate) || feeRate <= 0)
-                feeRate = 1m;
+            if (!CoinAmount.TryParseFeeRate(SendFeeRate, out var feeRate))
+            {
+                DonatePreview = Loc.Tr("msg.feerate.invalid");
+                return;
+            }
 
             _pendingDonate = new TransactionFactory(_account).Build(
                 _doc.Cache.Utxos, _lastTransactions, destination, amount, feeRate,

src/App/ViewModels/MainWindowViewModel.Send.cs

@@ -74,7 +74,7 @@ public partial class MainWindowViewModel
                 SendPreview = Loc.Tr("msg.amount.invalid");
                 return;
             }
-            if (!decimal.TryParse(SendFeeRate, out var feeRate) || feeRate <= 0)
+            if (!CoinAmount.TryParseFeeRate(SendFeeRate, out var feeRate))
             {
                 SendPreview = Loc.Tr("msg.feerate.invalid");
                 return;

src/Cli/Program.cs

@@ -217,7 +217,9 @@ static async Task<int> Send(string[] o)
     long amount = 0;
     if (!sendAll && !CoinAmount.TryParseCoins(Opt(o, "--amount") ?? "", out amount))
         throw new WalletSpendException("--amount missing or invalid (or use --all).");
-    var feeRate = decimal.TryParse(Opt(o, "--feerate"), out var fr) ? fr : 1m;
+    var feeRate = 1m;
+    if (Opt(o, "--feerate") is { } feeText && !CoinAmount.TryParseFeeRate(feeText, out feeRate))
+        throw new WalletSpendException($"--feerate invalid (expected sat/vB in (0, {CoinAmount.MaxFeeRate}]).");
 
     // Source transactions of the UTXOs: needed for amounts and signing.
     await using var client = await Connect(o, account.Profile);

src/Core/Wallet/CoinAmount.cs

@@ -80,4 +80,25 @@ public static class CoinAmount
         }
         return true;
     }
+
+    /// <summary>Upper bound accepted for a fee rate, in sat/vB (guards against typos).</summary>
+    public const decimal MaxFeeRate = 1000m;
+
+    /// <summary>
+    /// Parses a fee rate in sat/vB, independent of the system culture. Accepts a decimal point or
+    /// comma; rejects thousands separators, exponents, signs, zero and values above
+    /// <see cref="MaxFeeRate"/>.
+    /// </summary>
+    public static bool TryParseFeeRate(string? text, out decimal satPerVbyte)
+    {
+        satPerVbyte = 0;
+        if (text is null)
+            return false;
+        text = text.Trim().Replace(',', '.');
+        if (!decimal.TryParse(text, NumberStyles.AllowDecimalPoint, CultureInfo.InvariantCulture, out var rate)
+            || rate <= 0 || rate > MaxFeeRate)
+            return false;
+        satPerVbyte = rate;
+        return true;
+    }
 }

tests/PalladiumWallet.Tests/Wallet/CoinAmountTests.cs

@@ -5,6 +5,67 @@ namespace PalladiumWallet.Tests.Wallet;
 
 public class CoinAmountTests
 {
+    // ---- fee rate (sat/vB): culture-independent ----
+
+    [Theory]
+    [InlineData("1", "1")]
+    [InlineData("1.5", "1.5")]
+    [InlineData("1,5", "1.5")]
+    [InlineData("0.5", "0.5")]
+    [InlineData("  2 ", "2")]
+    [InlineData("2.25", "2.25")]
+    [InlineData("1000", "1000")]
+    public void TryParseFeeRate_accepts_valid(string text, string expected)
+    {
+        Assert.True(CoinAmount.TryParseFeeRate(text, out var rate));
+        Assert.Equal(decimal.Parse(expected, System.Globalization.CultureInfo.InvariantCulture), rate);
+    }
+
+    [Theory]
+    [InlineData("1.000")] // looks like a thousands separator in it-IT/de-DE but is 1.000 → accepted as 1
+    public void TryParseFeeRate_dot_is_always_decimal(string text)
+    {
+        Assert.True(CoinAmount.TryParseFeeRate(text, out var rate));
+        Assert.Equal(1m, rate);
+    }
+
+    [Theory]
+    [InlineData("1e3")]
+    [InlineData("-1")]
+    [InlineData("+1")]
+    [InlineData("0")]
+    [InlineData("0.0")]
+    [InlineData("1000.01")]
+    [InlineData("1,000.5")]
+    [InlineData("1 000")]
+    [InlineData("abc")]
+    [InlineData("")]
+    [InlineData(null)]
+    public void TryParseFeeRate_rejects_invalid(string? text)
+    {
+        Assert.False(CoinAmount.TryParseFeeRate(text, out var rate));
+        Assert.Equal(0m, rate);
+    }
+
+    [Theory]
+    [InlineData("it-IT")]
+    [InlineData("de-DE")]
+    [InlineData("fr-FR")]
+    [InlineData("en-US")]
+    public void TryParseFeeRate_ignores_current_culture(string culture)
+    {
+        var saved = System.Globalization.CultureInfo.CurrentCulture;
+        try
+        {
+            System.Globalization.CultureInfo.CurrentCulture = new System.Globalization.CultureInfo(culture);
+            Assert.True(CoinAmount.TryParseFeeRate("1.5", out var a));
+            Assert.True(CoinAmount.TryParseFeeRate("2,25", out var b));
+            Assert.Equal(1.5m, a);
+            Assert.Equal(2.25m, b);
+        }
+        finally { System.Globalization.CultureInfo.CurrentCulture = saved; }
+    }
+
     // ---- valid amounts: all units ----
 
     [Theory]