[GUI] Added localization support, more clean design, and improved settings management (#119)

* [GUI] Added localization support, more clean design, and improved settings management

* reuse

src/SharpEmu.GUI/Localization.cs

@@ -0,0 +1,109 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+using System.Text.Json;
+
+namespace SharpEmu.GUI;
+
+/// <summary>
+/// Loads UI strings for the launcher from Languages/&lt;code&gt;.json next to the
+/// executable. The files are plain, pretty-printed JSON (a flat key/value
+/// map) so they stay easy to open and translate by hand; a missing or
+/// unreadable key falls back to the key name itself.
+/// </summary>
+public sealed class Localization
+{
+    public static Localization Instance { get; } = new();
+
+    public sealed record LanguageInfo(string Code, string NativeName);
+
+    private Dictionary<string, string> _strings = new();
+
+    private Localization()
+    {
+    }
+
+    /// <summary>Directory holding the *.json language files; user-editable.</summary>
+    public static string LanguagesDirectory => Path.Combine(AppContext.BaseDirectory, "Languages");
+
+    public string CurrentCode { get; private set; } = "en";
+
+    public string Get(string key) => _strings.TryGetValue(key, out var value) ? value : key;
+
+    public string Format(string key, params object?[] args) => string.Format(Get(key), args);
+
+    /// <summary>Languages discovered under <see cref="LanguagesDirectory"/>, sorted by code.</summary>
+    public List<LanguageInfo> DiscoverLanguages()
+    {
+        var languages = new List<LanguageInfo>();
+        try
+        {
+            foreach (var file in Directory.EnumerateFiles(LanguagesDirectory, "*.json"))
+            {
+                var code = Path.GetFileNameWithoutExtension(file);
+                languages.Add(new LanguageInfo(code, ReadLanguageName(file) ?? code));
+            }
+        }
+        catch (Exception)
+        {
+            // Missing Languages directory: no languages to offer.
+        }
+
+        languages.Sort((a, b) => string.CompareOrdinal(a.Code, b.Code));
+        return languages;
+    }
+
+    private static string? ReadLanguageName(string path)
+    {
+        try
+        {
+            using var document = JsonDocument.Parse(File.ReadAllText(path));
+            if (document.RootElement.TryGetProperty("_languageName", out var name) &&
+                name.ValueKind == JsonValueKind.String)
+            {
+                return name.GetString();
+            }
+        }
+        catch (Exception)
+        {
+            // Malformed file: fall back to the file's code as its display name.
+        }
+
+        return null;
+    }
+
+    /// <summary>Loads a language by file code (e.g. "en"), falling back to English.</summary>
+    public void Load(string code)
+    {
+        if (!TryLoadFile(code) && !string.Equals(code, "en", StringComparison.OrdinalIgnoreCase))
+        {
+            TryLoadFile("en");
+        }
+    }
+
+    private bool TryLoadFile(string code)
+    {
+        try
+        {
+            var path = Path.Combine(LanguagesDirectory, $"{code}.json");
+            if (!File.Exists(path))
+            {
+                return false;
+            }
+
+            var loaded = JsonSerializer.Deserialize<Dictionary<string, string>>(File.ReadAllText(path));
+            if (loaded is null)
+            {
+                return false;
+            }
+
+            _strings = loaded;
+            CurrentCode = code;
+            return true;
+        }
+        catch (Exception)
+        {
+            return false;
+        }
+    }
+}