Stop the wizard asking for a language it cannot apply

Picking English in the installer produced a German program, which reads like
a bug and is not one: the [Languages] choice localises the wizard, while
MateFan reads CurrentUICulture at every start and follows the Windows
display language.

ShowLanguageDialog defaults to yes, so the question was always asked. Turned
off, the wizard falls back to LanguageDetectionMethod=uilanguage — the same
signal the program uses — and the two now always agree. Nobody is asked
something whose answer expires with the last wizard page.

The readme gains a Language section, because "which language will I get" is
a user question and it was only answered under Development notes.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0154ydCSH6y6ha5Dp3GUQHKA

Author: shockwave-coder

README.md

@@ -64,6 +64,12 @@ attached to every release:
 > Get-FileHash .\MateFan-Setup-1.0.0.exe -Algorithm SHA256
 > ```
 
+### Language
+
+MateFan is English and German, and it follows your **Windows display language** — decided fresh at
+every start, not fixed at install time. Change the display language and MateFan follows on the next
+start. Any display language other than German gets the English interface.
+
 ### Administrator rights
 
 MateFan always runs elevated, because the firmware interface it uses requires it. That is also why

installer/matefan.iss

@@ -41,6 +41,15 @@ SetupIconFile=..\src\MateFan.App\assets\matefan.ico
 UninstallDisplayIcon={app}\{#AppName}.exe
 LicenseFile=..\LICENSE
 
+; Do not ask. The wizard's language would only ever apply to the wizard: MateFan reads
+; CurrentUICulture at every start, so the installed program follows the Windows display language
+; whatever was picked here. Asking a question whose answer expires with the last wizard page is
+; how a user ends up choosing English and getting a German program.
+;
+; With the dialog off, LanguageDetectionMethod defaults to uilanguage — the same signal MateFan
+; uses — so the wizard and the program now always agree.
+ShowLanguageDialog=no
+
 [Languages]
 Name: "english"; MessagesFile: "compiler:Default.isl"
 Name: "german"; MessagesFile: "compiler:Languages\German.isl"

tests/MateFan.Tests/InstallerScriptTests.cs

@@ -26,6 +26,17 @@ public void The_post_install_launch_keeps_setups_elevated_credentials()
         Assert.Contains("runascurrentuser", run);
     }
 
+    /// <summary>
+    /// The wizard must not offer a language choice. It would apply to the wizard alone — MateFan
+    /// reads CurrentUICulture at every start — so a user could pick English and watch a German
+    /// program start on the next page. Off, the wizard detects the same UI language the app does.
+    /// </summary>
+    [Fact]
+    public void The_wizard_does_not_offer_a_language_choice_it_cannot_honour()
+    {
+        Assert.Matches(@"(?m)^\s*ShowLanguageDialog\s*=\s*no\s*$", Script);
+    }
+
     /// <summary>The installer only notices a running MateFan if both names agree exactly.</summary>
     [Fact]
     public void The_installer_watches_the_mutex_the_application_holds()