Add detailed guidelines for localization string formatting and usage patterns

Author: johlju

.github/instructions/dsc-community-style-guidelines-localization.instructions.md

@@ -8,3 +8,28 @@ applyTo: "source/**/*.ps1"
 All message strings for Write-Debug, Write-Verbose, Write-Error, Write-Warning
 and other error messages in classes, public commands and private functions should
 be localized using localized string keys.
+
+## String File Format
+```powershell
+# Localized resources for <ResourceName>
+ConvertFrom-StringData @'
+    KeyName = Message with {0} placeholder. (PREFIX0001)
+'@
+```
+
+## String ID Format
+Use unique IDs: `(PREFIX####)`
+- PREFIX: First letter of each word in resource name or function name
+- ####: Sequential number starting 0001
+- Examples: SqlSetup → SS0001, SqlAGDatabase → SAGD0001, Get-SqlDscSqlDatabase → GSDSD0001
+
+## Usage Patterns
+```powershell
+# Verbose/Warning messages
+Write-Verbose -Message ($script:localizedData.KeyName -f $value)
+Write-Warning -Message ($script:localizedData.KeyName -f $value)
+
+# Error messages
+New-InvalidOperationException -Message ($script:localizedData.KeyName -f $value1, $value2)
+New-InvalidOperationException -ErrorRecord $_ -Message ($script:localizedData.KeyName -f $value1)
+```