Fixes issues where lua uses the C# default locale instead of the invariant locale (C)

src/Lua/Standard/Internal/DateTimeHelper.cs

@@ -1,3 +1,4 @@
+using System.Globalization;
 using System.Runtime.CompilerServices;
 using System.Text;
 
@@ -165,14 +166,14 @@ static void ThrowInvalidConversionSpecifier(LuaState state, ReadOnlySpan<char> f
             var pattern = STANDARD_PATTERNS(c);
             if (pattern != null)
             {
-                builder.Append(d.ToString(pattern));
+                builder.Append(d.ToString(pattern, CultureInfo.InvariantCulture));
             }
             else
                 switch (c)
                 {
                     case 'e':
                     {
-                        var s = d.ToString("%d");
+                        var s = d.ToString("%d", CultureInfo.InvariantCulture);
                         builder.Append(s.Length < 2 ? $" {s}" : s);
                         break;
                     }
@@ -184,10 +185,10 @@ static void ThrowInvalidConversionSpecifier(LuaState state, ReadOnlySpan<char> f
                         break;
                     case 'C':
                         // TODO: reduce allocation
-                        builder.Append((d.Year / 100).ToString());
+                        builder.Append((d.Year / 100).ToString(CultureInfo.InvariantCulture));
                         break;
                     case 'j':
-                        builder.Append(d.DayOfYear.ToString("000"));
+                        builder.Append(d.DayOfYear.ToString("000", CultureInfo.InvariantCulture));
                         break;
                     case 'u':
                     {
@@ -197,13 +198,13 @@ static void ThrowInvalidConversionSpecifier(LuaState state, ReadOnlySpan<char> f
                             weekDay = 7;
                         }
 
-                        builder.Append(weekDay.ToString());
+                        builder.Append(weekDay.ToString(CultureInfo.InvariantCulture));
                         break;
                     }
                     case 'w':
                     {
                         var weekDay = (int)d.DayOfWeek;
-                        builder.Append(weekDay.ToString());
+                        builder.Append(weekDay.ToString(CultureInfo.InvariantCulture));
                         break;
                     }
                     case 'U':

src/Lua/Standard/Internal/IOHelper.cs

@@ -1,3 +1,4 @@
+using System.Globalization;
 using Lua.Internal;
 using Lua.IO;
 
@@ -70,7 +71,7 @@ CancellationToken cancellationToken
                 {
                     using PooledArray<char> fileBuffer = new(64);
                     var span = fileBuffer.AsSpan();
-                    d.TryFormat(span, out var charsWritten);
+                    d.TryFormat(span, out var charsWritten, provider: CultureInfo.InvariantCulture);
                     await file.WriteAsync(
                         fileBuffer.UnderlyingArray.AsMemory(0, charsWritten),
                         cancellationToken

tests/Lua.Tests/DateTimeTests.cs

@@ -1,6 +1,7 @@
 using Lua.Platforms;
 using Lua.Standard;
 using Microsoft.Extensions.Time.Testing;
+using System.Globalization;
 
 namespace Lua.Tests;
 
@@ -57,6 +58,28 @@ public async Task OsDate_WithExplicitTime_UsesThatTime()
         Assert.That(result[0], Is.EqualTo(new LuaValue("2000")));
     }
 
+    [Test]
+    public async Task OsDate_UsesCLocaleForNames()
+    {
+        var culture = CultureInfo.CurrentCulture;
+        CultureInfo.CurrentCulture = CultureInfo.GetCultureInfo("de-DE");
+        try
+        {
+            var state = LuaState.Create();
+            state.OpenOperatingSystemLibrary();
+
+            // 946771200 is the unix time for 2000-01-02 00:00:00 UTC
+            var result = await state.DoStringAsync("""return os.date("!%A %B", 946771200)""");
+
+            Assert.That(result, Has.Length.EqualTo(1));
+            Assert.That(result[0], Is.EqualTo(new LuaValue("Sunday January")));
+        }
+        finally
+        {
+            CultureInfo.CurrentCulture = culture;
+        }
+    }
+
     [Test]
     public async Task OsDateTable_RoundTripsThroughOsTime()
     {